Lake County is located in the state of Montana. As of 2000, the population is 26,507. Its County Seat is Polson. Much of Lake County Montana resides within the boundaries of the Flathead Indian Reservation. From the County Seat of Polson Montana, the Mission Mountain Range borders Lake County to the east, Flathead Lake to the North, the Mission Valley to the south and Irvine Flats to the west.