Warm River is a city in Fremont County, Idaho, United States. The population was 3 at the 2010 census, making it the least populous city in Idaho. It is part of the Rexburg, Idaho Micropolitan Statistical Area. History Warm River was incorporated in the 1940s in order to bring the small resort community in compliance with state law restricting liquor licenses to only incorporated municipalities. Geography Warm River is located at (44.114560, -111.317528). According to the United States Census Bureau, the city has a total area of , of which, is land and is water. Demographics 2010 census As of the census of 2010, there were 3 people, 2 households, and 0 families residing in the city. The population density was . There were 5 housing units at an average density of . The racial makeup of the city was 100.0% White. There were 2 households, of which 100.0% were non-families. 50.0% of all households were made up of individuals, and 50% had someone living alone who was 65 years of age or older. The average household size was 1.50 and the average family size was 0.00. The median age in the city was 56.5 years. 0.0% of residents were under the age of 18; 0.0% were between the ages of 18 and 24; 0 were from 25 to 44; 2 were from 45 to 64; and 1 were 65 years of age or older. The gender makeup of the city was 1 male and 2 female. 2000 census As of the census of 2000, there were 10 people, 3 households, and 3 families residing in the city. The population density was 13.6 people per square mile (5.2/km). There were 4 housing units at an average density of 5.4 per square mile (2.1/km). The racial makeup of the city was 100.00% White. There were 3 households, out of which none had children under the age of 18 living with them, 33.3% were married couples living together, 33.3% had a female householder with no husband present, and 0.0% were non-families. The average household and family size was 3.33. In the city, the population was spread out, with 30.0% from 18 to 24, 20.0% from 25 to 44, 10.0% from 45 to 64, and 40.0% who were 65 years of age or older. The median age was 45 years. For every 100 females, there were 150.0 males. For every 100 females age