Census webinar walks users through ACS API basics, endpoints, and UCGID tips

Caleb Hoppler, supervisory survey statistician in the American Community Survey Office at the U.S. Census Bureau, and Joseph Booth, supervisory IT specialist, presented a webinar demonstrating how to access ACS data through the Census Bureau data API and shared practical tips for developers and data users.

"The API gives software and web developers the ability to create and easily update custom application[s]," Hoppler said, framing the API as a central way to retrieve both historical and current ACS tables not always visible on data.census.gov. He reminded users that API requests start with api.census.gov/data/{year}/{dataset} and that the query must include ?get= with the variables and geography predicates they need. Hoppler also explained the three parts of an ACS variable ID—table ID, row number and annotation—and noted that annotations ending in "e" return estimates while "m" returns margins of error.

Why it matters: ACS is the primary ongoing source of detailed social, economic and housing data used in federal funding formulas and local planning. Hoppler noted the survey samples "approximately 3 and a half million addresses each year," and that ACS produces 1‑year and 5‑year period estimates with different geographic coverage.

Booth emphasized endpoint differences and developer pitfalls, showing that some API root endpoints return multiple datasets in JSON and that responses can be returned in HTML, JSON or XML. He demonstrated the examples and geographies endpoints and how to read JSON responses to see which predicate fields are required (for example, specifying a county value generally requires also specifying the state). "UCGID is very, very powerful," Booth said, demonstrating how adding geo_id (Uniform Census Geographic identifier) to a call makes programmatic swaps of jurisdictions straightforward and makes code more robust.

The presenters ran a county-level example using table B01001 and DeKalb County, Alabama, and showed how adding descriptive=true to a request returns human-readable labels alongside cryptic variable names. They advised users to limit calls to 50 variables per query and to register for a free API key if they expect more than 500 calls per day.

Hoppler also previewed subject-matter additions to ACS: electric vehicles, solar panels and public sewer connectivity were added as topics in 2025, with data for these topics planned for release in 2026. He reviewed the release cadence, reminding users that ACS estimates are released the year after data are collected and that 1‑year estimates are available for geographies with populations of 65,000 or more (with supplemental 1‑year tables available for some geographies of 20,000 or more) while 5‑year estimates cover smaller geographies.

The webinar included a practical walkthrough of data.census.gov’s table UI and its built-in API tool, which lets users copy a ready-made API URL for the selected geography. Presenters recommended using the API discovery tool at api.census.gov/data to explore available datasets, the groups endpoint to find variables more efficiently than the full variables listing, and the UCGID for programmatic workflows.

Resources and next steps: presenters pointed listeners to the developers page at census.gov/developers, Census Academy training, an updated introductory webinar scheduled for Aug. 20, an API workshop with sign-ups opening Aug. 6, a recently published API tutorial video, Slack-based developer support and a help contact at acso.users.support@census.gov (phone: 809238282). The webinar recording, transcript and slides will be posted on the Census website.

The recorded webinar concluded with a Q&A invitation and a reminder that the slides and recording will be available for later review.