78% of the population in Deli Serdang Regency is Muslim.

The Muslim population in Deli Serdang Regency, as of December 31, 2023, was recorded at 1.6 million people. This is an increase of 34,917 individuals compared to the previous year, which reported 1.56 million.

According to data from the Directorate General of Population and Civil Registration (Ditjen Dukcapil) of the Ministry of Home Affairs, the proportion of the Muslim population in this regency/city reached 78 percent of the total population in 2024, which numbered 2.05 million.

If expressed as a percentage of the population of each area in North Sumatra, the Muslim population in Deli Serdang Regency ranks second.

Below is the population of North Sumatra by religion in 2023:

* Islam: 1,596,546 (78.0%)
* Protestant: 336,163 (16.42%)
* Catholic: 56,220 (2.75%)
* Buddhist: 38,916 (1.9%)
* Hindu: 2,808 (0.14%)
* Indigenous Beliefs: 236 (0.01%)
* Confucianism: 133 (0.01%)

Other regencies/cities in North Sumatra with the largest Muslim populations are: Medan City (1,764,738), 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), North Labuhan Batu Regency (330,029), and South Labuhan Batu Regency (281,302).