[3][4] Mille Lacs County is included in the Minneapolis-St. Paul Metropolitan Statistical Area.

A portion of the Mille Lacs Indian Reservation is in the county.

The Rum River flows south through the county, originating from Mille Lacs Lake.

It is joined by the West Branch of the Rum River, which rises in northwest Mille Lacs County and flows south-southeast to its confluence with the Rum at Princeton.

The county terrain consists of wooded rolling hills, carved by drainages, with open areas devoted to agriculture.

[6] The terrain slopes to the south and east,[7] with its highest point at one mile (1.6 km) from the southwest shoreline of Mille Lacs Lake, in Mille Lacs Kathio State Park.

25.90% of all households were made up of individuals, and 12.00% had someone living alone who was 65 years of age or older.

Mille Lacs County voters have traditionally voted a balanced ticket, but in the past few decades have become strongly Republican.