Island Park is a city in Fremont County, Idaho, United States. The city's population was 193 at the 2020 census, down from 286 in 2010. The city was incorporated by owners of the many lodges and resorts along U.S. Route 20 in 1947, primarily to circumvent Idaho's liquor laws that prohibited the sale of liquor outside of city limits. It is only 500 feet (150 m) wide in most locations and at 33 miles (53 km), claims to have the longest "Main Street" in the world.