About Public Use Microdata Areas (PUMAs)

Public Use Microdata Areas (PUMAs) divide states into geographic areas containing no fewer than 100,000 and no more than 200,000 people. Because they are required to have this minimum population of 100,000, PUMAs exceed the 65,000 population threshold for American Community Survey 1-year estimates. PUMAs generally follow county and census tract boundaries and are redefined every 10 years after the decennial census.

PUMAs are geographic areas defined specifically for the distribution of PUMS data from the decennial census, ACS, and the Puerto Rico Community Survey. PUMS data are individual records about characteristics of people and housing stripped of personal identifying information. PUMS data allow for more detailed and complex research techniques, but the files are more difficult to work with than published tables. For example, data users need to use statistical software, such as SPSS, SAS, R, or Stata to process PUMS data.

PUMAs allow data users to make statistical analysis and comparisons because these areas have almost identical population numbers. PUMAs also allow users to create estimates and measures with combinations of person/household variables that are not available elsewhere. And as stated above, dividing geographic areas into PUMAs also ensures that data for these areas will be included in ACS 1-year estimates so will reflect the most timely data available.

PUMAs generally follow the boundaries of county groups and census tracts, and these groupings (unless islands) must share a border. However, if these areas exceed 200,000 residents, they are then divided into as many PUMAs of more than 100,000 residents as possible. IN this way more densely populated areas, like Chicago and Cook County will contain many PUMAs within their boundaries, while multiple sparsely populated entire counties, e.g., Jackson, Perry, Franklin, and Williamson, will comprise one PUMA.

While PUMAS can cross county lines, PUMAS do not cross state lines. In this way, PUMAs nest within Illinois and look generally like larger block-like collection of counties when viewed on a map.

The map below shows PUMAs outlined in orange. Other geographic regions can be toggled on and off to view how they fit within or across PUMAs. Note that this PUMA map represents the current PUMA boundaries, which are based on the 2020 full-count census. These boundaries were released in 2022. For the year 2021 and earlier, PUMA boundaries are based on the 2010 census.