Average Family Size

As related to the Total Family Households
Compiled using estimates from the American Community Survey, 5-Year, 2009-2013
United States
American Community Survey, 5-Year

This is a choropleth map that colors counties by average family size. Note that average values are used, which is why the scale includes fractions. The author is aware that the idea of a fractional person unit is ridiculous.

The pattern of increasing average family size as you move north to south appears to be inversely related to median age.