Data sources and methodology

The numbers on our county pages come from public data. Here's exactly what we use and how to read it.

Housing and population

U.S. Census Bureau, American Community Survey (ACS) ACS 2024 5-year estimates covering 2020-2024, accessed through Census Reporter. Tables used:

• B01003 total population, B01002 median age
• B25001 housing units, B25002 occupancy, B25003 tenure
• B25024 units in structure (single-family and mobile homes)
• B25034 and B25035 year structure built
• B25040 house heating fuel
• B25077 median home value, B19013 median household income

ACS figures are survey estimates with margins of error, which are larger in smaller counties. A "state county median" means the median across all of that state's counties, not the statewide total.

Weather

Daily county averages for 2015–2024 from NOAA's nClimGrid-Daily dataset (EpiNOAA county series), published by NOAA's National Centers for Environmental Information on the AWS Open Data registry. nClimGrid interpolates daily station observations onto a roughly 5-kilometer grid, and the county series averages that grid over each county. From daily minimum and maximum temperature and precipitation we count:

• Freezing nights: days with a low at or below 32°F.
• Pipe-freeze nights: days with a low at or below 20°F.
• Freeze-thaw days: a low at or below 32°F and a high above 32°F on the same day.
• Longest cold spell: most consecutive days with a high at or below 32°F.
• Heavy-rain days: days with 1 inch or more of precipitation, plus the wettest single day and three-day total.
• Muggy nights: days with a low of 65°F or more, a simple sign of humid summer air.
• First and last freeze: the average date of the first fall and last spring night at or below 32°F.

Because the values are averaged across each county, low spots, ridgetops and lakeshores can be colder or warmer than the county figure. The data has no humidity or snowfall, so we don't publish those.

Boundaries and neighbors

County and place boundaries are from Census TIGER files (U.S. Census Bureau TIGER boundaries via Census Reporter). Neighboring counties share a boundary. Communities are Census places whose center falls inside the county, ranked by population.

Coverage

We currently publish 2,285 county pages across 25 states and add more as the data and call coverage are ready. Data last generated 2026-10-21.