The Red Lake River flows southward into the county from Pennington County. It is joined near Red Lake Falls by the Clearwater River; the combined flow (still known as the Red Lake River) flows southwestward to Huot, where it is augmented by the Black River, which drains the northwestern part of the county. The Red Lake River then flows southwestward into Polk County. The county terrain consists of low rolling hills, etched by drainages and gullies. The area is devoted to agriculture. The county terrain slopes to the west, with its highest elevation on its southeastern corner, at 1,201' (366m) ASL. The county has a total area of , of which is land and (0.02%) is water.