The checker, the radius search, and the county reports all stop at the same 500 counties. Expanding to all 3,144 U.S. counties is a later job. Adjacent suburbs are the usual miss.
What 500 is. The largest counties by ACS population, enough to cover most large metros and many of their inner suburbs. It is not a random sample of America, and it is not every county in those metros. Houston’s postal city already spans several counties; some of those are in, some may sit on the edge.
When the checker says a ZIP is not covered, the honest next step is a nearby covered ZIP or city — not a guess. We do not fill missing counties with estimates.
File-count limits on the host also cap how many county pages can be added at once. Coverage grows when a data window and the file budget both allow it, not because a ZIP looked empty.
If your ZIP misses, try the city name. If the city spans a covered county, the checker lists those ZIPs. County reports stay the administrative unit; the city grouping is postal.
Cite: BizGapMap, “The 500-county edge”, https://bizgapmap.com/stories/the-500-county-edge/. Census ZBP 2023, ACS 2024 5-year. Supply counts, not advice. Reuse and CSV →
BizGapMap — free, no-login small-business saturation reports for major U.S. counties. Built entirely from public U.S. Census, BLS, and IRS data (ZBP 2023, ACS 2024 5-year, PEP 2024, LODES, QCEW, IRS SOI). No forecasts, no revenue guesses — withheld cells are marked, and the few derived counts are labelled as estimates.