Donora is located at 40°10′33″N  / –79°51′41″W (40.175879, −79.861264).

According to the United States Census Bureau, the borough has a total area of 2.0 square miles (5.2 km2), of which 1.9 square miles (4.9 km2) is land and 0.2 square miles (0.5 km2) (7.32%) is water.

The climate in this area is characterized by hot, humid summers and generally mild to cool winters. According to the Köppen Climate Classification system, Donora has a humid subtropical climate, abbreviated “Cfa” on climate maps.