Harlowton is a city in and the county seat of Wheatland County, Montana, United States. The population was 955 at the 2020 census. The city was once the eastern terminus of electric operations for the "Pacific Extension" of the Chicago, Milwaukee, St. Paul and Pacific Railroad. Here, steam or diesel locomotives were changed or hooked up to electric locomotives for 438-mile trip through the Rocky Mountains to Avery, Idaho.