Monument Mountain is a 2.5-mile (4.0 km) long quartzite ridgeline located in Great Barrington and Stockbridge, Massachusetts in the Berkshires geology.

Flag Rock, located on the southwest side of the mountain, is an open ledge overlooking the village of Housatonic.

The only official trails on the mountain ascend Peeskawso Peak from a parking lot on Massachusetts Route 7 north of Great Barrington center.

The west side of Monument Mountain drains into the Housatonic River thence into Long Island Sound.

In August 1850, Herman Melville, Nathaniel Hawthorne and Oliver Wendell Holmes Sr. climbed Monument Mountain together.