96.7% of the population in Indragiri Hilir Regency is Muslim.

The Muslim population in Indragiri Hilir Regency as of December 31, 2023, was recorded at 681,930. Compared to the previous year, the number of Muslims in the regency/city increased by 18,547.

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 96.7 percent of the total population in 2024, which numbered 705,040.

Considering its distribution relative to the population of each area in Riau, the proportion of Muslims in Indragiri Hilir Regency ranks third.

Below is the population of Riau by religion in 2023:
* Islam 681,926 (96.72%)
* Protestant 8,525 (1.21%)
* Buddhist 4,160 (0.59%)
* Catholic 910 (0.13%)
* Indigenous Beliefs 30 (0.0%)
* Hindu 20 (0.0%)
* Confucian 0 (0.0%)

Compared to other regions in Riau, the Muslim population in this regency/city is among the top three.

Other areas with the top 10 Muslim populations in Riau province are: Pekanbaru City 949,432, Kampar Regency 766,783, Rokan Hilir Regency 583,466, Bengkalis Regency 540,601, Rokan Hulu Regency 485,636, Indragiri Hulu Regency 426,403, Siak Regency 393,038, Pelalawan Regency 336,994, Kuantan Singingi Regency 336,947, and Dumai City 291,583.