Gallatin County averaged about 15 permitted housing units per 1,000 residents annually from 2016 to 2020. Missoula County ranked next among the state’s six largest counties in 2021-2025, with 8.5 permitted units per 1,000 residents. Gallatin County planning official Ashlie Burke said housing costs are shaped by what affordable-housing advocates sometimes call the “three Ls”: land, lumber and lending. Faust said it’s not common that a housing project is abandoned after permits are issued, but it does sometimes happen. Billings’ certificate-of-occupancy records shared with MTFP also show how large apartment projects can make the annual count of permitted housing units swing.