Ismay is a town in Custer County, Montana, United States. The population was 19 at the 2010 census. The town is the smallest 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 (later president) of the Chicago, Milwaukee and St. Paul Railway. Other communities with related names include Earling, Iowa; Marmarth, North Dakota; and Alberton, Montana. As a publicity stunt coordinated by the Kansas City Chiefs in 1993, the town unofficially took the name of Joe, Montana, after the NFL quarterback Joe Montana.
The town's history and contemporary state (circa 1995) is discussed at length in travel writer Jonathan Raban's book, Bad Land: An American Romance. According to Raban, Ismay's story is emblematic of the settlement and desettlement of the northern Great Plains.