 According to the U.S. Census Bureau, the county has a total area of , of which is land and (6.0%) is water.It is the largest of Rhode Island's five counties by land area.The county is drained by the Blackstone River, which runs partly along the east border, the Woonasquatucket River in the central part of the county, joining with the smaller Moshassuck River in downtown Providence, and the Pawtuxet, which forms a portion of the southeastern boundary of the county.