Half of Americans live in 145 US counties

The 50 states and the District of Columbia hold 3,142 counties between them. 145 of those counties hold half the country's residents. The smaller half of the list, 1,571 counties, holds 5.5 per cent of them. Los Angeles County reports 9,848,406 residents and Kalawao County reports 43, and both count once in a county average.

So a measure quoted per county and the same measure quoted per person are two different answers to two different questions. Neither is wrong. They are not interchangeable, and most plans need the second one.

Income, where the two answers sit furthest apart

The middle county reports a median household income of $63,672. The middle resident lives in a county reporting $78,204, which is Providence County in Rhode Island, 22.8 per cent higher and $14,532 a year apart. Only 574 counties, 18.3 per cent of the list, report $78,204 or more, and between them they hold 50.2 per cent of the population.

The line between the two halves of the population runs through Polk County in Iowa, the 145th largest at 497,441 residents, $81,621 and 10.1 per cent poverty. Everything above it on the size list holds the first half of the country.

Poverty is the exception

Weighting does not move every measure. The middle county reports 13.2 per cent of residents in poverty. The middle resident lives in a county reporting 12.2 per cent, Broward County in Florida, and the rate across the whole population is 12.5 per cent. That is about a point, against nearly a quarter on income.

The reason is that poverty is spread more evenly across the size range than income is. The 1,571 smallest counties hold 5.5 per cent of residents and 6.8 per cent of residents in poverty. The 145 largest hold 50.1 per cent of residents and 48.2 per cent of those in poverty. Small counties are poorer on the middle figure, 13.8 per cent against 13.2 per cent for the full list, but there are not enough people in them to shift the national rate.

Attainment and connection follow income

Two more measures move the way income does. Degree-level attainment reads 21.4 per cent for the middle county and 34.8 per cent for the middle resident, whose county is Dallas County in Texas, a gap of 13.4 points. Household broadband reads 85.3 per cent against 90.7 per cent, the second figure belonging to Queens County in New York. In each case the county list is the more cautious number and the population is the more connected one, because the large counties sit at the top of both.

What this changes for a plan

Two decisions usually rest on a number like this: where to spend, and what to assume about the people there. A market sizing built on the middle county is built on a place of about 25,822 residents, and it understates household income by $14,532. A plan that instead assumes the population figure will overstate income and attainment everywhere outside the largest 145 counties. The fix is not to pick the better average. It is to carry the counties separately for as long as the decision allows, which is what place-based analysis is for.

Cambium AI builds synthetic populations from this same public data, so a research or marketing team can hold every county side by side instead of choosing one headline figure. The figures here come from the American Community Survey, the Census Bureau's annual household survey, and how that survey is turned into a population, weighting included, is set out in the methodology.

Data source: U.S. Census Bureau, American Community Survey (ACS) 5-Year Estimates