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.
The unorganized area is gradually being reduced in size. In 1971, a portion was added to Lake of Bays Township in Muskoka District, and between 1996 and 2001, its area shrunk from to , because of annexation by surrounding incorporated townships.
Localities located within the unorganized area are:
The following geographic townships are included:
All, except Boulter, Lauder, and parts of Ballantyne, Boyd and Paxton are within Algonquin Provincial Park.
Most of the population lives outside of Algonquin Park on the northern or northwestern fringes of the region. According to the 2016 Census, the blocks that encompass the Townships of Boulter, Lauder, Pentland and Boyd had a combined population of 57. The area around Loxton Lake in Ballantyne Township (Census Block 35480228012) had a population of 26. Census Block 35480228215 which covers parts of Bronson and Stratton Townships in the Northeast corner of Algonquin Park had a population of 5, while 15 people lived in Census Block 35480228146 which covers most of the western part of the region.