[3] Clay County is part of the Fargo, ND-MN Metropolitan Statistical Area.

The county's government was not organized until 1872, after the Northern Pacific Railway reached the area and settlement accelerated.

The Red River flows northward along the western boundary line of the county, on its way to the Hudson Bay in Canada.

The Buffalo River flows west-northwesterly through the center of the county, joined by the South Branch Buffalo River west of Glyndon, before discharging into the Red on the county's western border near Georgetown.

The terrain consists of rolling hills, dotted with lakes and ponds in its eastern portion.

[6] The terrain slopes to the west and north, with its highest point near the southeastern corner, at 1,430 ft (440 m) ASL.

26.10% of all households were made up of individuals, and 10.60% had someone living alone who was 65 years of age or older.