Built with a unique crescent moon shape, Fort Popham was a result of the countries concerns about the naval ships of the Confederacy during the time of the Civil War. The fort was constructed in 1862, using granite blocks obtained from Fox and Dix Island. The granite blocks actually form the 30-foot walls of Fort Popham, which faced the Kennebec River.

Fort Popham was only activated during the time of the Spanish-American War, and was reactivated during the First World War When Fort Baldwin was later constructed, Fort Popham was left obsolete since the former had guns that have longer range and were more powerful. Nevertheless, Fort Popham became a famous spot for tourists where people can either enjoy having picnic or going fishing.