Flat Willow Colony is a Hutterite community and census-designated place (CDP) in Musselshell County, Montana, United States. It is in the northern part of the county, east of U.S. Route 87 and north-northeast of Roundup, the Musselshell county seat.
The community was first listed as a CDP prior to the 2020 census, at which time it had a population of 15.
According to the U.S. Census Bureau, the colony has an area of , all land.