Muscongus Bay is a bay on the coast of Maine, United States, between Penobscot Bay and Johns Bay. John Smith recorded the river in 1616 as Nusconcus and was also spelled Nuscongus. The two main tributaries are the Saint George River at its eastern end and the Medomak River, which flows into the bay at Waldoboro. Historically, the Medomak River and Muscongus Bay were the dividing line between the Waldo Patent and Pemaquid Patent and Waldoboro was a customs point of entry. Muscongus Bay has many islands including Hog which is home to a National Audubon Society camp, Allen, Eastern Egg Rock, Franklin, and Louds Island historically referred to as Muscongus Island prior purchase from Thomas Drowne by William Loud. Monhegan Island is offshore from Muscongus Bay. The Maine Island Trail passes through Muscongus Bay.
