Research Guides: US Census and Demographic Information: Understanding Census Geography

Introduction to Census Geography

Understanding Census geography is not always as simple as it would seem. There are traditional methods for dividing up geography in the United States that most people are familiar with, such as states, counties, and zip codes. The Census uses its own methods and terminology for geography as well, the most prominent of which is a division known as a "Census tract," which divides up counties. The links on this page are provided to help users comprehend Census geography and how it can be used to better understand population and demographic data.

The following image offers a basic outline of Census geographic divisions. Definitions of many of the terms in the diagram are in this Census geography glossary.

Additional Current & Historical Resources

Geographic Terms and Concepts
This resource provides detailed explanations of Census geography, including Census tracts, Census blocks, Native American tribal areas, school districts, and others.
2020 Census Geographic Areas Reference Maps
PDFs from the U.S. Census Bureau displaying "counties, county subdivisions, places consolidated cities and American Indian areas/Alaska Native areas/Hawaiian home lands" by state. Also includes US territories.
The reference maps were formerly referred to as the State/County Subdivision Outline Maps.
Guide to state and local census geography (2011)
Has information about the census geography of each state for the 2010 Census

Map Guide to the U. S. Federal Censuses, 1790-1920 by William Thorndale; William Dollarhide
Call Number: Dimond Reference Desk G1201.F7 T5 1992
ISBN: 0806311886
Publication Date: 2005
The county has always been used as the basic Federal census unit. This work shows all U.S. county boundaries from 1790 to 1920. On each of the nearly 400 maps the old county lines are superimposed over the modern ones to highlight the boundary changes at ten-year intervals. Then there is an index listing all present-day counties, plus nearly all defunct counties or counties later re-named. With each map there is data on boundary changes, notes about the census, and locality finding keys.