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U.S. Census Research Guide

The U.S. Census Bureau conducts several data collection programs about the U.S. population which have their own language, geography, and data portals. This guide is based on a similar guide created by Kelly Smith at UCSD.

About the ACS

About the American Community Survey (ACS)

The American Community Survey (ACS) is an ongoing survey conducted by the U.S. Census Bureau since 2005. In 2010, the ACS replaced the Decennial Census long form as the source of sample data for population and housing indicators. The short form of the Decennial Census is still distributed to obtain a count of the entire U.S. population.

ACS asks questions about age, sex, race, family and relationships, income and benefits, health insurance, education, veteran status, disabilities, employment location and mode of travel to work, place of residence, price paid for living essentials. You can review the annual questionnaires to see the precise questions asked each year.

There are both benefits and challenges associated with replacing the long form with ACS. The primary benefit is the freshness of data: ACS data is collected every year, whereas the decennial Census was collected every ten years. Challenges include a higher sampling error for the ACS, due to a smaller sample population, and difficulties comparing data from year to year.

Finding ACS Statistics & Data

Census Bureau

ACS data is incorporated into data.census.gov, the Census Bureau's primary data tool, with a variety of access points:

The Census Bureau provides Guidance for Data Users, options to download data via FTP, and Public Use Microdata Samples (PUMS).

Using American Community Survey Data with Open-Source Software:  examples of open-source libraries and packages (R, Python, JavaScript) for working with ACS data that have been created by developers in the data user community.

Library Databases

NUSearch lists several ACS briefs and reports, most of which are available online.  ACS Reports are also provided by the Census Bureau.  Examples of titles produced in 2015 -- Who Drives to Work?; Young Adult Migration; Remarriage in the United States.

Open Access

Creating an account is required

ACS Estimates & Comparisons

ACS Estimates

Each year, the Census Bureau releases 1- and 5-year estimates based on information gathered in the ACS.  3-year estimates were discontinued in 2014.  Data from the 3-year estimates collected 2005-2013 will remain available, e.g. 2005-2007, 2006-2008, 2007-2009, 2008-2010, 2009-2011, 2010-2012, 2011-2013.

In deciding which estimate you want to use, you should consider a) the currency of data; b) the geographic size of your population; and c) the acceptable sample size/reliability of the data.  The Census Bureau chart below shows distinguishing features of the different estimates.

Important note: if you wish to compare ACS estimates to earlier decennial Census data, please review these cautions first.

  • Comparing ACS Estimates
  • Statistical Test Tool to determine the significance of data compared
  • Comparitive tables are available in the American FactFinder - use the Advanced Search and enter these table numbers:
    • CP02 - Social Characteristics
    • CP03 - Economic Characteristics
    • CP04 - Housing Characteristics
    • CP05 - Demographic Characteristics

Understanding and Using American Community Survey Data: What All Users Need to Know.  [PDF July 2018]