US Census and American Community Survey

The American Community Survey

This page has information about the American Community Survey (ACS), an ongoing and continuous survey since 2005 that replaced the decennial census long form as the collection device for more detailed information about the US population than the standard decennial census.

The page has the following learning objectives:

• Compare the differences between the United States Decennial Census and the American Community Survey
• Understand the methodology of data collection and what that means for scholarly research
• Interpret margin of error in ACS data
• Determine whether 1-, 3-, or 5-year summary ranges are appropriate for your research

The American Community Survey

The American Community Survey (ACS) is an ongoing survey that provides vital information on a yearly basis. Information from the survey generates data that help determine how more than $675 billion in federal and state funds are distributed each year. [source]

Every year, the Census Bureau contacts over 3.5 million households across the country to participate in the ACS using a random sample of addresses. The information is used by government agencies, nongovernmental organizations, planners, tribal governments and organizations, businesses, researchers, journalists, and the public. [source]

Those already familiar with the US Census may recall that during the 20th century the questions were divided between a short form and a long form, where the short form asked basic questions about age, sex, race, and key housing questions. The long form asked more detailed questions but was only required of a subset of households. The 2010 decennial census used only the short form and the long form was replaced by the ACS. [source]

Check out the first couple minutes of the video below to get a broad overview of the ACS. Watch the whole thing to get an introduction to topics such as survey ranges and census geographies.

Survey Methodology and Margins of Error in the ACS

The American Community Survey (ACS) is not a full count of the population like the Decennial Census. Instead, it’s a survey that collects detailed data from a sample of about 3.5 million households each year. That means its results are estimates, not exact numbers.

Because the ACS is based on a sample, every estimate comes with a Margin of Error (MOE). This tells you how much the true value might vary from the reported number. Smaller areas (like census tracts or block groups) usually have larger margins of error because fewer people were surveyed there.

Why it matters:

• If you're comparing two areas, overlapping margins of error might mean there's no meaningful difference between them.
• The ACS is still a powerful tool—but it's important to use it carefully, especially for small populations or geographies.

Tips for working with ACS data:

• Use 5-Year Estimates for small areas—they combine multiple years of data for better accuracy.
• Always check the MOE column in downloaded tables.
• Use charts or maps to show patterns—but be cautious when interpreting fine-grained differences.

Want more detail? Check out the ACS Technical Documentation or explore tools like MOE calculators from the Census Bureau.

ACS Data by Geography: What You Can Get Where

The American Community Survey (ACS) publishes two main types of estimates: 1-Year and 5-Year. These differ not just in how current they are, but also in what geographic levels they’re available for.

Here’s a quick comparison to help you decide which dataset fits your project:

*Data at the block group level includes fewer variables and greater margins of error. Use with caution, especially for comparisons.

Summary: Use 1-Year Estimates for large areas when you need the most recent data. Use 5-Year Estimates for detailed geographic breakdowns, small towns, and tracts—even though they average data across time.

Explore ACS data using: data.census.gov or Social Explorer.

What Can You Learn from Census and ACS Data?

The U.S. Census and the American Community Survey (ACS) are both valuable sources of information—but they collect different types of data for different purposes. Here’s a quick guide to what you’ll find in each:

While the Census gives a complete count of the U.S. population, the ACS provides detailed, yearly information based on a sample. For small geographic areas or detailed questions, the ACS 5-year estimates are usually your best bet.

Want to explore these topics? Try tools like Social Explorer, data.census.gov, or NHGIS.