Big Falls is a city in Koochiching County, Minnesota, United States. The population was 175 at the 2020 census. U.S. Highway 71 and Minneā¦Big Falls is a city in Koochiching County, Minnesota, United States. The population was 175 at the 2020 census. U.S. Highway 71 and Minnesota State Highway 6 are two of the main routes in Big Falls. A post office called Big Falls has been in operation since 1906. The city was named for a nearby waterfall on the Big Fork River.