Barrett Mountain is a mountain located in south-central New Hampshire within the Wapack Range of mountains. It lies within the town of New Ipswich and is traversed by the 22-mile (35 km) Wapack Trail. Kidder Mountain is located directly to the north along the Wapack ridgeline; New Ipswich Mountain to the south. The summit of the mountain is mostly wooded. A cross-country ski area occupies the north side of Barrett Mountain.
The east side of the mountain drains into the Souhegan River watershed, to the Merrimack River thence the Atlantic Ocean; the northwest side drains into the Gridley River, to the Contoocook River thence into the Merrimack River; the southwest side drains into the Millers River watershed, to the Connecticut River, thence into Long Island Sound.