Phillips County is a county in the U.S. state of Montana. As of the 2020 census, the population was 4,217. Its county seat is Malta. Before February 5, 1915, Phillips County was part of Blaine County, and before 1912 both were part of Chouteau County. It was named for rancher and state senator Benjamin D. Phillips. Its northern boundary is the Canada–United States border with Saskatchewan. The Missouri River defines its southern boundary.