 According to the U.S. Census Bureau, the county has a total area of , of which is land and (1.6%) is water.Notable physical features include the Allegheny River, the Allegheny Reservoir, the Kinzua Dam, and the Allegheny National Forest.The county has a warm-summer humid continental climate ("Dfb") and average temperatures in the city of Warren range from 24.5 °F in January to 69.3 °F in July.