Harrison is a census-designated place in Madison County, Montana, United States. The population was 137 at the 2010 census, according to factfinder.censu.gov.Harrison is located at 45°42′9″N 111°47′7″W / 45.70250°N 111.78528°W / 45.70250; -111.78528.According to the United States Census Bureau, the CDP has a total area of 0.2 square miles, all of it land.As of the census of 2000, there were 162 people, 64 households, and 44 families residing in the CDP. The population density was 704.9 people per square mile. There were 75 housing units at an average density of 326.3 per square mile. The racial makeup of the CDP was 96.91% White, 1.85% Native American, 0.62% Asian, and 0.62% from two or more races. Hispanic or Latino of any race were 1.23% of the population.There were 64 households out of which 39.1% had children under the age of 18 living with them, 56.3% were married couples living together, 9.4% had a female householder with no husband present, and 29.7% were non-families. 25.