Census Bureau’s Urban and Rural Classification and 

Overview of 2020 Urban Area Criteria

Federal Committee on Statistical Methodology Annual Research and Policy Conference

Washington, DC

October 26, 2022

Michael Ratcliffe

Geography Division

U.S. Census Bureau

The views expressed in this presentation are those of the author 

and not necessarily those of the U.S. Census Bureau.
Introduction

• The history of the Census Bureau’s urban-rural classification since the late- 19th century has been one of response to: 

• Changes to settlement patterns in and around cities.

• Changes in theoretical approaches to interpreting and understanding the 

growth of urban areas.

• Improved technology (i.e., GIS, digital databases) making it easier to 

manage large amounts of data.

• Increased spatial resolution of statistical and geospatial data.

• For information on the history of the Census Bureau’s urban and rural 

classification, see: “A Century of Delineating a Changing Landscape,” 

https://www2.census.gov/geo/pdfs/reference/ua/Century_of_Defining_

Urban.pdf

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Census Bureau Urban Areas: 2010 Definition

• Urbanized areas: 50,000 or more population.

• Urban clusters: at least 2,500 and less than 50,000 

population.

• Defined primarily based on population density 

measured at the census tract and census block 

levels.

• Initial urban core: at least 1,000 per square mile 

• Remainder of urban area: at least 500 per square mile

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*2020 ACS estimates for urban areas are based on urban area boundaries 

defined in 2010 and do not account for new urbanization that occurred 

outside those boundaries between 2010 and 2020.

2010 Census 

Population

2010 

Percent

2020 ACS 5-

year 

Population 

Estimates*

2020 

Percent

Total 308,745,538 100.0 326,569,308 100.00

Urban 249,253,271 80.7 263,366,402 80.7

Urbanized Area 219,922,123 71.2 233,777,857 71.6

Urban Cluster 29,331,148 9.5 29,588,545 9.1

Rural 59,492,267 19.3 63,202,906 19.3

Sources: 2010 Census; 2016-2020 ACS 5-year data.
• Urban Areas of at least 2,000 housing units or at least 5,000 people.

• Defined primarily based on housing unit density measured at the census block 

level.

• Initial urban core: at least 425 housing units per square mile

• Remainder of urban area: at least 200 housing units per square mile

• At least one high density nucleus of at least 1,275 housing units per square mile required 

for qualification.

Census Bureau Urban Areas (2020 Census criteria)

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Key Changes to Urban Area Criteria

• Minimum threshold for qualification as urban: at least 2,000 housing units or at least 5,000 

population. Increased from a minimum of 2,500 persons.

• Use of housing unit density at the census block level instead of population density.

• No longer distinguish between urbanized areas of 50,000 or more population and urban clusters 

of less than 50,000 persons.

• Maximum distance for “jumping” across low-density intervening territory reduced from 2.5 miles 

to 1.5 miles (return to the jump distance that was in effect from 1950 through 1990).

• Will not include the intervening low-density “hop” and “jump” corridors in the urban area. This 

results in noncontiguous urban areas.

• Splitting continuous urban agglomerations based on commuting patterns (using Longitudinal 

Employer-Household Dynamics [LEHD] data).

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Change to Thresholds for Qualifying as an Urban Area

• Minimum threshold for qualification as urban: at least 2,000 housing units or at least 5,000 

population. Increased from a minimum of 2,500 persons.

• 2,500-person threshold had been in use since 1910. 

• Census Bureau’s threshold was the lowest in use in various agencies’ urban/rural definitions.

• Rural stakeholders and analysts have questioned the continued validity of the 2,500-person 

threshold and have routinely asked if we would consider an increase. Most recently, the 

Western Governors’ Association asked us to consider raising the threshold to 10,000 persons.

• Impact:

• Approximately 1,000 areas in the US would shift from urban to rural status (based on 2016-

2020 ACS 5-year data). These areas contained an estimated 3.5 million people in 2020 (ACS 

2016-2020 5-year estimates).

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Why 2,500 persons?

• The Census Bureau officially adopted the 2,500-person threshold as the minimum population for 

an urban place in 1910.

• Truesdell, 1949: “For the census of 1910 the definition of urban population [2,500 persons] presented 

in the [1906] Statistical Analysis was adopted, again without any discussion of its merits as compared 

with those which had been used earlier; and this definition has been used, with minor modifications, in 

later censuses down to and including 1940.”

• From 1874 to 1900:

• 1874: 8,000-person threshold was used to identify urban cities and towns.

• 1880: 4,000-person threshold. “It seemed to be the opinion of the officials in charge of the census in 

1880 that the 8,000 limit was too high to include all of the population that was really urban in 

character.” (Truesdell, 1949).

• 1890: back to 8,000 persons.

• 1900: 4,000-person threshold used in reports.

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Source: Leon Truesdell, 1949. “The Development of the Urban-Rural Classification in the 

United States: 1874 to 1949.” Current Population Reports, P-23, Number 1.
All other changes to criteria and population distribution aside, the 

change to the minimum threshold will result in an increase in rural 

population.

Urban and Rural Population 

Based on 2010 Threshold 

Urban and Rural Populations 

Based on 2020 Thresholds 

Applied to Current Urban Areas

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2016-2020 ACS 

5-year Population 

Estimates 2020 Percent

United States 326,569,308 100.0

Urban 263,366,402 80.7

Rural 63,202,906 19.3

2016-2020 ACS 5-year 

Population Estimates 2020 Percent

United 

States 326,569,308 100.0

Urban 259,850,930 79.6

Rural 66,718,378 20.4

Source: 2016-2020 ACS 5-year data.
Urban areas that had 2010 Census populations of 2,500 up to 9,999, as a category, 

lost population between 2010 and 2020. All other size categories experienced 

population increases.

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Sources: 2010 Census; 2016-2020 ACS 5-year data.

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

1 million+ 500,000 to 999,999 250,000 to 499,999 100,000 to 249,999 50,000 to 99,999 25,000 to 49,999 10,000 to 24,999 5,000 to 9,999 2,500 to 4,999

Percent Change in Urban Area Population, 

2010 to 2020, by Size Category

(percent change for US as a whole = 5.8)
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Housing Unit Density

More direct 

measure of 

developed 

landscape

425 housing units per 

square mile (HPSM) 

for initial cores

200 HPSM to fill in 

extent of urban areas

1,275 HPSM to ensure 

each urban area has a 

high-density nucleus

Census blocklevel housing unit 

counts are 

invariant

Ability to update 

extent of Urban 

Areas between 

censuses

200 HPSM = 500 persons per square mile (PPSM), based on national average of 2.5 persons per housing unit

425 HPSM = 1,062 PPSM

1,275 HPSM = 3,188 PPSM
Use of housing unit density at the census block-level provides the ability to 

update urban area boundaries between censuses. 

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Post-2010 development on 

the west side of the San 

Antonio urban area. 

Because urban areas are 

not updated between 

censuses, the population 

and housing in this and 

similar areas was treated 

as rural in American 

Community Survey and 

other statistical data 

products.
No Longer Distinguish Between Types of Urban Areas

No longer distinguish between urbanized areas of 50,000 or more population and urban clusters of less than 

50,000 persons.

• No clear scientific basis for use of 50,000 as a threshold distinguishing different types of urban areas.

• The decision to adopt 50,000 as a threshold for urbanized areas starting in 1950 seems to have been 

based more on operational concerns and data availability than rooted in economic data or central place 

theory. 

• Urban areas between 40,000 and 51,000 population are similar in terms of economic activity.

• Still possible for data users and agencies to identify areas based on various sizes of population.

Impact: The term “Census Bureau-defined urbanized areas” is used in legislation and program documentation 

without specific reference to population size since urbanized areas, by definition, had a minimum population 

of 50,000. These references will have to be revised to “... urban areas of 50,000 or more...” or interpreted to 

mean areas of 50,000 or more persons.

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Urban areas with populations just above or just below the 50,000-person 

threshold do not differ substantially in terms of economic activity, as measured 

by numbers of firms and retail sales.

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Data for each urban area are based on the aggregation of data for places located 

within the urban area (Economic Census data are not tabulated for urban areas). 
Change to Jump Distance and Inclusion of Intervening Low-Density Territory

• Maximum distance for “jumping” across low-density intervening territory reduced from 2.5 miles to 1.5 

miles (return to the jump distance that was in effect from 1950 through 1990).

• Will not include the intervening low-density “hop” and “jump” corridors in the urban area. This results in 

noncontiguous urban areas.

Impact: 

• Will reduce the amount of land area within individual urban areas. This will have a positive impact on the 

measurement of the extent of urbanization and urban sprawl.

• Will affect the total population of individual urban areas. A small number of areas might drop below 50,000 

persons as a result.

• Creation of noncontiguous areas adds complexity when using our areas.

• Use of geographic information systems mitigates the complexity of working with complicated 

boundaries.

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By not including hop and jump corridors, low-density areas with typically rural land uses will not be included in 

the urban area, resulting in a more accurate delineation.

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Splitting Urban Agglomerations

• The delineation process results in large 

agglomerations encompassing multiple, individual 

urban areas. The question each decade is how, 

and where, to split these large agglomerations to 

define more recognizable and meaningful areas 

for analysis.

• Previous decades’ delineations relied on 

metropolitan area definitions (which had 

been based on the previous decade’s urban 

area boundaries) or where the connecting 

corridor was narrowest. None of these 

approaches were data driven.

• For 2020, we will use the Longitudinal EmployerHousehold Dynamics (LEHD) Origin-Destination 

(LODES) dataset to analyze commuting patterns to 

determine whether to split agglomerations and, if 

so, where to draw the boundary.

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Contiguous urban areas in the Baltimore and Washington areas.
Is it time to consider a continuum of categories?

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For more information:

https://www.census.gov/programssurveys/geography/guidance/geo-areas/urbanrural.html

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Michael Ratcliffe

Senior Advisor

Geography Division

michael.r.ratcliffe@census.gov

Thank You. Questions? 

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