Island Park is a city in Fremont County, Idaho, United States. The city's population was 286 at the 2010 census, up from 215 in 2000. 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 yet, at 33 miles (53 km), claims to have the longest "Main Street" in the world.

Fremont County is a county located in the U.S. state of Idaho. As of the 2020 census the county had a population of 13,388. The county seat and largest city is St. Anthony. The county was established in 1893, and was named for the explorer John C. Frémont. Fremont County is part of the Rexburg, Idaho micropolitan area, which is also included in the Idaho Falls metropolitan area.