80.5% of the population in South Tapanuli Regency is Muslim.

The Muslim population in South Tapanuli Regency, as of December 31, 2023, was recorded at 255,340. This is an increase of 5,035 individuals compared to the previous year, which reported 250,300.

According to data from the Directorate General of Population and Civil Registration (Ditjen Dukcapil) of the Ministry of Home Affairs, the proportion of Muslims in this regency/city reached 80.5 percent of the total population in 2023, which numbered 317,080.

Based on the distribution across districts in North Sumatra, the proportion of Muslims in South Tapanuli Regency ranks 14th.

The population of North Sumatra by religion in 2023 was:

* Islam: 255,339 (80.53%)
* Protestant: 60,422 (19.06%)
* Catholic: 4,219 (1.33%)
* Buddhist: 6 (0.0%)
* Hindu: 0 (0.0%)
* Confucian: 0 (0.0%)
* Indigenous Beliefs: 0 (0.0%)

Compared to other regions in North Sumatra, the Muslim population in this regency/city ranks 14th out of 33 regencies/cities in North Sumatra province.

Other areas with the largest Muslim populations in North Sumatra province are: Medan City (1,764,738), Deli Serdang Regency (1,596,546), Langkat Regency (1,013,445), Asahan Regency (713,024), Simalungun Regency (584,987), Serdang Bedagai Regency (582,369), Mandailing Natal Regency (475,115), Labuhan Batu Regency (426,629), Batu Bara Regency (410,553), and Labuhan Batu Utara Regency (330,029).