Acadia National Park is a national park located in the U.S. state of Maine. It reserves much of Mount Desert Island, and associated smaller islands, off the Atlantic coast. Created when a national monument after three years became Lafayette National Park in 1919, it was renamed Acadia in 1929 and is the oldest American national park east of the Mississippi River, (third including Canada, following Thousand Islands (1904) and Point Pelee (1918) in Ontario).