The Mercer Union Meetinghouse is a historic church on Main Street, just west of United States Route 2, in Mercer, Maine. Built in 1829 for several different denominations to share, this church is a relatively early and rare example of transitional Federal-Gothic styling in the state, with its tower set partially over the entrance vestibule, another uncommon feature. The building was listed on the National Register of Historic Places in 2007.