In 2021, Mandailing Natal had the largest Muslim population in North Sumatra.

The majority of the population in Mandailing Natal Regency practices Islam. Based on data from the Directorate General of Population and Civil Registration (Dukcapil) of the Ministry of Home Affairs, the Muslim population in the regency was 469,900 in December 2021.

This represents 95.92% of the total population of 489,910. This percentage is the highest compared to the other 32 regencies/cities in North Sumatra.

The next highest percentage of Muslims is in Langkat Regency, with 977,460 people (91.71%). This is followed by Padang Sidempuan City with 206,780 people (90.58%).

In contrast, the percentage of Muslims in Nias Regency is only 1,670 people (1.15%) of a total population of 145,320. This is the lowest percentage among all regions.

Following this are Samosir Regency with 2,480 Muslims (1.75% of the total population), and West Nias Regency with 2,180 Muslims (2.25% of the total population).

The Muslim population of North Sumatra was 10.08 million last year. This accounts for 66% of the province's total population of 15.24 million.