Unorganized South Nipissing District is an unorganized area in north-central Ontario, in the District of Nipissing. It is almost entirely within and includes most of Algonquin Provincial Park.

Algonquin Provincial Park is an Ontario provincial park located between Georgian Bay and the Ottawa River, mostly within the Unorganized South Part of Nipissing District. Established in 1893, it is the oldest provincial park in Canada. Additions since its creation have increased the park to its current size of about 7,653 km2 (2,955 sq mi). The park is contiguous with several smaller, administratively separate provincial parks that protect important rivers in the area, resulting in a larger total protected area.