Ismay is a town in Custer County, Montana, United States. There is a post office at Ismay, and a church, and no other businesses or services. The population was 17 at the 2020 census. The town is the least-populous incorporated municipality in the state of Montana. The town's name is an amalgamation of Isabella and May, the names of the daughters of Albert J. Earling, division superintendent of the Chicago, Milwaukee and St. Paul Railway.