The mountain is located within the towns of Mount Washington, Massachusetts and Salisbury, Connecticut; much of it has been conserved as part of Massachusetts' Mount Washington State Forest and Connecticut's Mount Riga Forest Preserve. The south side of Round Mountain drains into Riga Lake and South Pond, then into Wachocostinook Brook, Salmon Creek, the Housatonic River, and Long Island Sound. The north side drains into Sages Ravine, thence into Schenob Brook, the Housatonic River, and Long Island Sound. Round Mountain is bordered by Mount Frissell to the northwest, Mount Ashley to the north, and Bear Mountain to the east.