South Tapanuli (Tapanuli Selatan in Indonesian Language, abbreviated Tapsel) is a regency in North Sumatra, Indonesia. Its seat is the town of Sipirok. This regency was originally very large and contained hundreds of towns and villages, including the city of Padang Sidempuan. The areas that have separated from South Tapanuli Regency are the new regencies of Mandailing Natal (created on 23 November 1998), Padang Lawas Utara, and Padang Lawas (both created on 17 July 2007), all lying to the south-east of the residual South Tapanuli Regency, plus the city (kota) of Padang Sidempuan (created on 21 June 2001). After the division, the regency seat moved from Padang Sidempuan to Sipirok.
The regency covers an area of 4,355.35 square kilometres and had a population of 264,108 at the 2010 census and 300,911 at the 2020 Census; the official estimate as at mid-2024 was 316,486 (comprising 159,420 males and 157,066 females). These figures exclude the city of Padang Sidempuan, which is virtually surrounded by South Tananuli territory but is independently administered.
