Atwood is a borough in Armstrong County, Pennsylvania, United States. The population was 112 at the 2020 census. Atwood is located at 40°44′58″N 79°15′51″W / 40.74944°N 79.26417°W in eastern Armstrong County. Pennsylvania Route 210 runs through the borough, leading 6 miles southwest to U.S. Route 422 at Elderton and 6 miles northeast …Atwood is a borough in Armstrong County, Pennsylvania, United States. The population was 112 at the 2020 census. Atwood is located at 40°44′58″N 79°15′51″W / 40.74944°N 79.26417°W in eastern Armstrong County. Pennsylvania Route 210 runs through the borough, leading 6 miles southwest to U.S. Route 422 at Elderton and 6 miles northeast to Plumville. Keystone Lake, a reservoir on the North Branch Plum Creek, runs near the northwestern border of the borough.