Cumston Hall is an historic library in downtown Monmouth, Maine. It was completed in 1900 and is named in honor of Dr. Charles M. Cumston, a former teacher at the English High School in Boston, who gave the Romanesque Revival and Queen Anne Style building to Monmouth equipped with a library and auditorium. Cumston chose Harry Hayman Cochrane (1860–1946), a muralist, to design and decorate it.
Today, Cumston Hall is the home of the Cumston Public library, the Theater at Monmouth, Monmouth Community Players, and many local activities. In the summer, the hall's auditorium becomes a series of grand theatrical performances from the Theater at Monmouth, in the business since 1970. This is the main draw for people living outside of Monmouth to come and see this landmark.
Cumston Hall has been on the United States National Register of Historic Places since the 1970s.