US Census ACS 5-year demographics for a state or county. Give a state (2-letter or 2-digit FIPS), optionally a 3-digit county FIPS, and get population, median age, median household income, per-capita income, poverty rate (computed), households, owner-occupancy rate (computed), median home value, and median gross rent. Free, public-domain (US Census Bureau). Complements census.zipcode (ZIP/ZCTA-level) with state- and county-level geography. Authoritative demographic data an LLM cannot recall — for market sizing, site selection, and socioeconomic research.