Documentation
Overview
The 2024 Urban Influence Codes are a nine-category county classification based initially on the Office of Management and Budget’s 2023 three classifications—metropolitan, micropolitan, and noncore counties:
- Metropolitan (metro) counties are divided into two categories based on the population size of the metro area (greater than or less than 1 million people).
- Micropolitan (micro) counties are divided into three categories based on their adjacency to metro areas of different sizes (adjacent to a large metro, adjacent to a small metro, and nonadjacent).
- Noncore nonmetropolitan (nonmetro) counties are divided into four categories based on their adjacency to large and small metro areas and the population size of their largest city or town (greater than or less than 5,000 residents).
Each county and census-designated county-equivalent in the United States is assigned a code, including those in outlying territories.
The topic page on Rural Classifications provides a summary of some of the many ways researchers and policy officials use different definitions to distinguish rural from urban areas, including the Rural Urban Continuum Codes and Urban Influence Codes.
Scope/Coverage
The 2024 Urban Influence Codes classify 3,235 counties and census-designated county-equivalents in the United States, including those in Puerto Rico, and entities in other outlying territories. County-equivalents (often included in the term "county" for ease of description), include parishes in Louisiana, municipios in Puerto Rico, and entities in other outlying territories. Nine Virginia independent cities were combined with their surrounding counties to determine their Urban Influence Code. These counties and independent cities share the same code but are reported separately, resulting in the total number of entities in the 50 U.S. States and the District of Columbia being 3,144.
The Urban Influence Codes were created in 1997 by Linda M. Ghelfi and Timothy S. Parker, then of the Economic Research Service (ERS), for their report A County-Level Measure of Urban Influence. ERS has published versions of the Urban Influence Codes based on data from 1993, 2003, 2013, and 2023, with changes to the methods in the 2003 and 2024 versions. While based on the same criteria as previous versions, the 2024 Urban Influence Codes have been rearranged, consolidated, and the town population threshold has been changed in response to changes in the Census Bureau's definition of urban areas, the continued expansion of metropolitan statistical areas in recent decades, and to make the codes more intuitive. All four versions of the Urban Influence Codes are in the file listing of this data product found on the opening page.
Methods
There are nine classifications in the 2024 Urban Influence Codes that are divided into three groups based on the county’s sphere of urban influence. The first group comprises codes 1–3 and identifies counties that are associated with large metropolitan areas with populations of at least 1 million residents. These are metro counties belonging to a large metro area (code 1), micropolitan (micro) counties adjacent to a large metro area (code 2), and noncore counties adjacent to a large metro area (code 3). The second group comprises codes 4–6 and identifies counties associated with small metropolitan areas with populations of less than 1 million people. These are metro counties belonging to a small metro area (code 4), micro counties adjacent to a small metro area (code 5), and noncore counties adjacent to a small metro area (code 6). The third group comprises codes 7–9 and identifies counties that do not belong to any metro area and that are not adjacent to any metro area. These are nonadjacent micro counties (code 7), nonadjacent noncore counties that contain all or part of a town with at least 5,000 residents (code 8), and nonadjacent noncore counties that do not have a town with at least 5,000 residents (code 9).
A county's designation as metropolitan (metro), micropolitan (micro), or noncore is based on the U.S. Office of Management and Budget’s (OMB) July 2023 delineation of core-based statistical areas. Metro areas are defined as broad labor-market areas that include central counties with one or more urban areas with populations of 50,000 or more people. Micro areas are defined as broad labor-market areas that include central counties with one or more urban areas with populations of at least 10,000 and fewer than 50,000 people. Metro and micro areas also include outlying counties that are economically tied to the central counties as measured by labor force commuting. OMB determined current metro and micro status using population and worker commuting criteria from the 2020 Census and the 2016–20 American Community Survey. A description of metro and micro area criteria is available in the OMB bulletin, 2020 Standards for Delineating Core Based Statistical Areas. For the purposes of this classification, noncore counties are defined by ERS as all counties that do not belong to any of the OMB-defined metro or micro areas.
Micropolitan and noncore counties are classified as metro adjacent if the county physically adjoins one or more metro areas and at least 2 percent of its employed labor force commutes to the central counties of the adjoined metro area. Counties that met the adjacency criteria to more than one metro area were designated as adjacent to the metro area to whose central counties the largest percentage of the adjacent county’s employed labor force commuted. County-level commuting data come from the 2016–20 American Community Survey and represent average commuting levels during that 5-year period.
Nonadjacent noncore counties are also differentiated by whether their largest town has a population of at least 5,000 people. A town refers to an incorporated place or a Census Designated Place (CDP) as defined by the U.S. Department of Commerce, Bureau of the Census (Census Bureau). The population threshold of 5,000 is used to reflect the Census Bureau’s 2020 definition of an urban area—a densely developed area with 2,000 or more housing units or 5,000 people.
Two methodological changes were made to the 2024 Urban Influence Codes in response to changes in the Census Bureau’s definition of urban areas, the continued expansion of metropolitan areas in recent decades, and to make the codes more intuitive:
- The codes were rearranged into three groups based on the sphere of urban influence that the counties belonged to: large metro, small metro, and nonadjacent. This was done to distinguish the Urban Influence Codes from other rural-urban classification systems such as the Rural-Urban Continuum Codes and to emphasize that the Urban Influence Codes are intended to identify hierarchical urban networks.
- The Urban Influence Codes were consolidated from the 12 categories used in the 2003 and 2013 versions to 9 categories in the 2024 version. Noncore counties adjacent to small metro areas are no longer distinguished by the size of their largest town and adjacency to micropolitan areas is no longer used to distinguish between noncore counties that are not adjacent to metro areas.
| Code | Description |
|---|---|
| Large metropolitan and adjacent counties | |
| 1 | Large metro (in a metro area with at least 1 million residents) |
| 2 | Micropolitan, adjacent to a large metro area |
| 3 | Noncore, adjacent to a large metro area |
| Small metropolitan and adjacent counties | |
| 4 | Small metro (in a metro area with fewer than 1 million residents) |
| 5 | Micropolitan, adjacent to a small metro area |
| 6 | Noncore, adjacent to a small metro area |
| Not adjacent to metropolitan counties | |
| 7 | Micropolitan, not adjacent to a metro area |
| 8 | Noncore, not adjacent to a metro area and contains a town of at least 5,000 residents |
| 9 | Noncore, not adjacent to a metro area and does not contain a town of at least 5,000 residents |
| Note: A county's designation as metropolitan, micropolitan, or noncore is based on the U.S. Office of Management and Budget’s July 2023 delineation of core based statistical areas. Micropolitan and noncore counties are classified as metro adjacent if the county physically adjoins one or more metro areas and at least 2 percent of its employed labor force commutes to the central counties of the adjoined metro area. Source: USDA, Economic Research Service using data from the Office of Management and Budget and U.S. Department of Commerce, Bureau of the Census. |
|
| Code | Number of counties | 2020 population |
|---|---|---|
| Large metropolitan and adjacent counties | 727 | 199,768,650 |
| 1 | 443 | 189,022,706 |
| 2 | 130 | 7,492,847 |
| 3 | 154 | 3,253,097 |
| Small metropolitan and adjacent counties | 1,505 | 116,913,224 |
| 4 | 743 | 96,626,916 |
| 5 | 272 | 12,185,521 |
| 6 | 490 | 8,100,787 |
| Not adjacent to metropolitan counties | 912 | 14,767,407 |
| 7 | 256 | 8,257,219 |
| 8 | 125 | 2,336,128 |
| 9 | 531 | 4,174,060 |
| U.S. total | 3,144 | 331,449,281 |
| Source: USDA, Economic Research Service using data from the Office of Management and Budget and U.S. Department of Commerce, Bureau of the Census. Population comes from the 2020 Census Demographic and Housing Characteristics File. | ||
| Code | Number of counties | 2020 population |
|---|---|---|
| Large metropolitan and adjacent counties | 45 | 2,193,037 |
| 1 | 40 | 2,081,265 |
| 2 | 3 | 88,744 |
| 3 | 2 | 23,028 |
| Small metropolitan and adjacent counties | 32 | 1,091,045 |
| 4 | 26 | 997,223 |
| 5 | 2 | 48,386 |
| 6 | 4 | 45,436 |
| Not adjacent to metropolitan counties | 12 | 339,813 |
| 7 | 0 | 0 |
| 8 | 4 | 244,975 |
| 9 | 8 | 94,838 |
| U.S. territory total | 89 | 3,623,895 |
| Note: U.S. territories included here are American Samoa, Guam, Northern Mariana Islands, Puerto Rico, and the U.S. Virgin Islands. Two county equivalents in American Samoa were not classified because they reported zero population in 2020. Source: USDA, Economic Research Service using data from the Office of Management and Budget and the U.S. Department of Commerce, Bureau of the Census. Population comes from the 2020 Census and 2020 Census Island Areas Demographic and Housing Characteristics Files. |
||
Strengths and Limitations
The Urban Influence Codes emphasize the role that neighboring urban areas have on rural counties by using adjacent metro size as a criterion for classifying nonmetro counties. Different sized cities offer different bundles of goods, services, and amenities. For example, a large metro area is more likely to have an international airport while a small metro area may only have a regional airport. Large metro areas are likely to have more specialized health care providers while a small metro area may only have a few health care specializations or more general health services (family and emergency medicine). The different bundles available in large metros and small metros may influence the economic, social, and health outcomes of nonmetro residents in adjacent counties as well as the perceived attractiveness of nonmetro counties for potential residents. The Urban Influence Codes enable researchers, policymakers, and others to examine these relationships.
Another contribution made by the Urban Influence Codes is the incorporation of both the OMB’s metropolitan statistical areas and its micropolitan statistical areas. Incorporating both of these definitions into the UIC classification allows researchers and policymakers to easily differentiate between metropolitan, micropolitan, and noncore counties even if they do not make full use of the UIC classification itself.
The Urban Influence Codes are assigned to county and county-equivalent geographies in the 50 States, Washington, D.C., Puerto Rico, and U.S. territories. Counties are a standard building-block for publishing economic data, which allows researchers and policymakers to apply the UIC to a wide range of policy issues and research questions. Although counties are more stable over time compared with other geographic units, changes to county boundaries do occur, which hampers longitudinal analysis. The largest such change occurred in 2022, when planning regions in Connecticut replaced counties in the Census Bureau’s county-level geography. To account for these changes, population figures for Connecticut’s planning regions were calculated using county subdivision data from the 2020 Decennial Census according to the Census Bureau’s County to County Subdivision Crosswalk file. Details and timing of county changes since 1970 can be found in this technical description of Substantial Changes to Counties and County Equivalent Entities: 1970–Present on the U.S. Census Bureau website.
Methodological changes made to the 2024 version of the Urban Influence Codes limit their comparability with previous versions:
- The town population threshold used to classify noncore counties that are not adjacent to metro areas was increased from 2,500 in the 2013 UIC to 5,000 in the 2024 UIC to reflect the changes made by the Census Bureau to its definition of urban areas (see Census Bureau’s 2020 definition of an urban area). This change results in an increase in the number of noncore counties that do not have a town with a population at or above the threshold and a decrease in the number of noncore counties with a town at or above the threshold.
- Some criteria used in previous versions of the UIC were removed to reduce the number of classifications from 12 to 9 and to make them more intuitive. Noncore counties adjacent to small metro areas are no longer differentiated by the size of their largest town and noncore counties that are not adjacent to metro areas are no longer differentiated by their adjacency to micro areas. These changes mean that the 2024 UIC is most comparable to the 1993 UIC.
- The UIC classifications were rearranged to emphasize nonmetro counties’ adjacency or non-adjacency to metro areas of different sizes.
| 2024 Code | 2024 Description | 2013 Code | 2013 Description |
|---|---|---|---|
| Large metropolitan and adjacent counties | |||
| 1 | Large metro (in a metro area with at least 1 million residents) | 1 | Large metro (in a metro area with at least 1 million residents) |
| 2 | Micropolitan, adjacent to a large metro area | 3 | Micropolitan, adjacent to a large metro area |
| 3 | Noncore, adjacent to a large metro area | 4 | Noncore, adjacent to a large metro area |
| Small metropolitan and adjacent counties | |||
| 4 | Small metro (in a metro area with fewer than 1 million residents) | 2 | Small metro (in a metro area with fewer than 1 million residents) |
| 5 | Micropolitan, adjacent to a small metro area | 5 | Micropolitan, adjacent to a small metro area |
| 6 | Noncore, adjacent to a small metro area | 6 | Noncore, adjacent to a small metro area and contains a town of at least 2,500 residents |
| 7 | Noncore, adjacent to a small metro area and does not contain a town of at least 2,500 residents | ||
| Not adjacent to metropolitan counties | |||
| 7 | Micropolitan, not adjacent to a metro area | 8 | Micropolitan, not adjacent to a metro area |
| 8 | Noncore, not adjacent to a metro area and contains a town of at least 5,000 residents | 9 | Noncore, adjacent to a micro area and contains a town of at least 2,500 residents |
| 11 | Noncore, not adjacent to a metro or micro area and contains a town of at least 2,500 residents | ||
| 9 | Noncore, not adjacent to a metro area and does not contain a town of at least 5,000 residents | 10 | Noncore, adjacent to a micro area and does not contain a town of at least 2,500 residents |
| 12 | Noncore, not adjacent to a metro or micro area and does not contain a town of at least 2,500 residents | ||
| Note: Metropolitan and micropolitan statistical areas are based on the U.S. Office of Management and Budget’s 2023 delineations of core based statistical areas. Counties are classified as 'adjacent' to a metro area if they are physically adjacent and at least 2 percent of their workforce commutes to the central counties of the physically adjacent metro area. Source: USDA, Economic Research Service, 2013 and 2024 Urban Influence Codes. |
|||
The 2003 and 2013 Urban Influence Codes can be cross walked into a configuration that is comparable to the 1993 and 2024 versions of the UIC by collapsing and rearranging categories, but the 2024 version cannot be converted to the 2003 and 2013 configuration. Comparability between the 2024 version and reconfigured previous versions is still limited by the change in the town population threshold from 2,500 to 5,000 in the 2024 version.
Data Sources
Office of Management and Budget, Metropolitan and Micropolitan Area Delineation Files, July 2023
U.S. Department of Commerce, Bureau of the Census, 2020 Census Demographic and Housing Characteristics File (DHC)
U.S. Department of Commerce, Bureau of the Census, 2020 Census Island Areas Demographic and Housing Characteristics File (DHC)
U.S. Department of Commerce, Bureau of the Census, County Adjacency File 2023
U.S. Department of Commerce, Bureau of the Census, County-to-County Commuting Flows: 2016–2020
U.S. Department of Commerce, Bureau of the Census, Connecticut County to County Subdivision Crosswalk
Recommended Citation
U.S. Department of Agriculture, Economic Research Service. (December, 2024). Urban Influence Codes.