PIGEON FORGE, Tenn.—Tom and Barb Hansen’s search for a retirement spot reads like the script to a road movie. California’s Lake Tahoe. Sedona and Scottsdale in Arizona. The Ozark Mountains of Missouri. Myrtle Beach, S.C.

Over a decade or so, the couple traveled the country to imagine life after Mr. Hansen retired as president of a community bank in the suburbs west of Chicago. In 2018, the Hansens, ages 61 and 60, picked rural Sevier County, Tenn.

A lot of other people had the same idea. Retirees are helping swell the population here to such an extent that Sevier County, along with a small number of other rural counties, aren’t only growing, but are adding residents at a faster clip than the U.S. overall, a Wall Street Journal analysis of the 2020 census found. Preliminary census estimates for those counties show the trend continuing into the pandemic.