Census — US Census Bureau

The official US Census Bureau data: decennial census, American Community Survey (ACS), economic census, population estimates, housing characteristics, geographic boundaries. National, state, county, place, tract, block-group, and ZCTA-level. Free, no key required for public datasets.

Part of Pipeworx — an MCP gateway connecting AI agents to 1476+ live data sources.

Why this matters for AI agents

Demographics, housing characteristics, economic activity, geographic identifiers — Census is the authoritative source. If an agent is computing per-capita rates, comparing metros, looking up population, or working with FIPS codes, this is where it goes.

Common flows:

Population for an area. ACS 1-year or 5-year estimates by state/county/place.
Housing characteristics. Median home value, occupancy, units, age — all in ACS.
Geographic ID lookup. Place name → FIPS code → boundary geometry.
Economic Census every 5 years for industry-level economic activity.

Pair with FRED for time-series macro and BLS for labor.

Auth

Most Census APIs are free and unauthenticated, with light rate limits (~500 calls/day per IP). For higher rates, get a key at https://api.census.gov/data/key_signup.html and pass via _apiKey.

Datasets worth knowing

Dataset	Cadence	Geography
Decennial Census (PL, DHC)	10-year	Block-level and up
ACS 5-year	Annually-rolling	Tract/BG (5-year smoothing)
ACS 1-year	Annually	Places ≥65k population
Population Estimates Program (PEP)	Annually	County-level
Economic Census	5-year	Industry × geography

ACS 5-year is what you usually want for current demographics — it's available at finer geographies than 1-year and updates yearly with rolling 5-year smoothing.

Common pitfalls

Year-of-coverage vs release year. ACS 5-year 2018-2022 was released in 2023. Don't conflate.
Margins of error. ACS includes MOE for every estimate. At small geographies (block group, small tract), MOEs can be larger than the estimate. Always carry MOE through to the user.
Geography hierarchy. State (01) → County (01001) → Tract (01001020100) → Block Group. The 11-digit tract code is state(2) + county(3) + tract(6).
Place vs MSA. "Denver" can mean the City and County of Denver, OR the Denver-Aurora-Lakewood Metropolitan Statistical Area (very different boundaries and populations). Disambiguate per use case.
Population estimates lag the decennial. Between censuses, PEP estimates are extrapolated and revised. The Census Bureau revises previous PEPs each year as they reconcile with births/deaths/migration data.

Quick Start

Add to your MCP client (Claude Desktop, Cursor, Windsurf, etc.):

{
  "mcpServers": {
    "census": {
      "url": "https://gateway.pipeworx.io/census/mcp"
    }
  }
}

What this endpoint actually serves

tools/list at https://gateway.pipeworx.io/census/mcp returns the tools in the table above plus the shared Pipeworx meta-tools — ask_pipeworx, discover_tools, search_within, remember/recall and the rest of the gateway-wide set. So the tool count you see is larger than this table: a single-pack endpoint currently lists roughly 30 shared tools alongside the pack's own. The connection's initialize response states its exact scope, and is the authoritative answer for a given day.

This is deliberate, not multiplexing by accident. The meta-tools are what let a scoped connection answer a question this pack does not cover — via ask_pipeworx, which routes across the whole catalog — without you adding a second MCP server. There is currently no way to mount a pack endpoint without them; if the extra schemas cost you more context than the routing is worth, connect to the full gateway once rather than to several pack endpoints.

Or connect to the full Pipeworx gateway to get every pack's tools listed directly, instead of just this one's:

{
  "mcpServers": {
    "pipeworx": {
      "url": "https://gateway.pipeworx.io/mcp"
    }
  }
}

Both URLs reach the same gateway and the same 1476+ data sources. The only difference is which pack's tools are listed directly; ask_pipeworx reaches all of them from either one.

Using with ask_pipeworx

Instead of calling tools directly, you can ask questions in plain English — this works on the pack endpoint above as well as on the full gateway:

ask_pipeworx({ question: "your question about Census data" })

The gateway picks the right tool and fills the arguments automatically.

License

MIT

Census