# US Counties and FIPS

County FIPS codes, names, areas, populations, centroids and density from US Census Bureau data.

## How to pay

Machine-payable over x402. USDC on: Base (eip155:8453), Solana (solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp), Polygon (eip155:137), Arbitrum One (eip155:42161).
No accounts. No API keys. No signup. The paying wallet is the account.

## Machine-readable

- OpenAPI: https://us-counties.x402tookit.com/openapi.json
- x402 manifest: https://us-counties.x402tookit.com/.well-known/x402
- Catalog (free): https://us-counties.x402tookit.com/catalog
- Health (free): https://us-counties.x402tookit.com/health
- Uptime (free): https://us-counties.x402tookit.com/uptime

## Endpoints (8)

### GET /counties-by-population — $0.02
Rank US counties by July 2025 population estimate, nationally or within one state; largest or smallest first.
Params: state?: string, order?: string, limit?: integer, offset?: integer
Example: https://us-counties.x402tookit.com/counties-by-population?limit=10

### GET /counties-in-state — $0.02
List a state's counties or county equivalents with FIPS, population and land area; resolves FIPS, postal code or name.
Params: state: string, sort?: string, limit?: integer, offset?: integer
Example: https://us-counties.x402tookit.com/counties-in-state?state=RI

### GET /county-density — $0.02
Population density of a US county per square mile and km of land, with national and state rank and US average.
Params: fips?: string, name?: string, state?: string
Example: https://us-counties.x402tookit.com/county-density?fips=36061

### GET /county-lookup — $0.02
US county by 5-digit FIPS or name plus state: name, area, population, density, centroid. Census Bureau data.
Params: fips?: string, name?: string, state?: string
Example: https://us-counties.x402tookit.com/county-lookup?fips=06037

### GET /county-nearest-to-point — $0.02
Counties whose Census centroids are nearest a latitude and longitude, with great-circle distance. Not point-in-polygon.
Params: lat: number, lon: number, limit?: integer
Example: https://us-counties.x402tookit.com/county-nearest-to-point?lat=41.8781&lon=-87.6298&limit=3

### GET /county-search — $0.02
Search US counties by full or partial name, optionally within one state; ranked, capped at 50.
Params: q: string, state?: string, limit?: integer
Example: https://us-counties.x402tookit.com/county-search?q=Washington&state=OR&limit=5

### GET /fips-parse-and-validate — $0.02
Split a county FIPS into state and county parts, check both exist, flag retired, legacy or zero-dropped codes.
Params: code: string
Example: https://us-counties.x402tookit.com/fips-parse-and-validate?code=36061

### GET /state-summary — $0.02
State totals from county data: county count, land and water area, population, density, largest and smallest counties.
Params: state: string
Example: https://us-counties.x402tookit.com/state-summary?state=TX

## Terms

Reference data from US Census Bureau Gazetteer files and Population Estimates (US public domain), provided as is. Counties and FIPS codes change; populations are July 1 estimates, not counts, and centroids are internal points, not addresses or boundaries. Not for legal, tax, voting or eligibility decisions; verify at census.gov.