Billings, Mont., is the new No. 1 on The Wall Street Journal/Realtor.com Emerging Housing Markets Index, boosted by its affordability and appeal to remote workers.

The index reflects how the housing boom has ignited homebuying activity in smaller to midsize cities around the U.S. The top 20 cities in the ranking have an average population size of just over 300,000.

In the latest index rankings published on Tuesday, smaller cities dominate. The No. 2 metro area is Coeur d'Alene, the lakeside Idaho city that held the top position when the index premiered in April. Fort Wayne, Ind., Rapid City, S.D., and Raleigh, N.C., round out the top 5.

The index identifies the top metro areas for home buyers seeking an appreciating housing market and appealing lifestyle amenities.