Cass County is included in the Brainerd, MN Micropolitan Statistical Area.

A substantial part of the Leech Lake Indian Reservation is in the county.

Cass County was created on September 1, 1851, by the Minnesota Territory legislature, although its government was not organized until 1897.

It was named for Lewis Cass, a Michigan political figure of the 19th century.

The Crow Wing River flows east-southeast along Cass County's southern border, and the Gull River flows southwest through the lower part, to discharge into the Crow Wing on the southern border.

The terrain consists of wooded rolling hills, heavily dotted with lakes and ponds,[6] and slopes to the south and east; its highest point is on the upper western border, at 1,614 ft (492 m) ASL.