The northern New England states lead the nation for the biggest percentage of vacation homes.

In Maine, 15.6 percent of 651,901 housing units are for seasonal use, followed by Vermont’s 14.6 percent of 294,382 homes and New Hampshire’s 10.3 percent of 547,024 homes.

The heaviest concentrations include an area that stretches across the forested northern regions of all three states.

In Maine, a large percentage of seasonal homes are in counties where the median household income is less than the median for a state as a whole – a pattern that holds across northern New England.

In Maine, 10.2 percent of seasonal homes are in counties where the median household income is less than the state median of $37,240. The figure is 11.3 percent for Vermont and 8.8 percent for New Hampshire.

Nationally, the figure is 2.2 percent.

In Piscataquis and Franklin, the counties with the highest percentage of seasonal homes in Maine, the median household income is $28,250 and $31,459, respectively, according to the census.

The value of homes is lower as well. The median housing values are $62,300 and $78,300, respectively, in the two counties, compared with the median value of $98,700 for Maine as a whole.