Warren County was formally organized in 1819.

The county seat is Warren.

According to the U.S. Census Bureau, the county has a total area of 898 square miles. Land comprises 883 square miles while 14 square miles is water.

Notable physical features include the Allegheny River, the Kinzua Dam, and the Allegheny National Forest. Warren County also contains a tract of old-growth forest called Hearts Content National Scenic Area.

There are five boroughs and twenty one townships in the county.