A list published by the centre which monitors extremist groups shows these 31 organisations are dotted across the world in an arc going from Algeria in the west to Indonesia in the east.
Abu Bakr al-Baghdadi, the head of IS which controls swathes of Syria and Iraq, proclaimed the establishment of an "Islamic caliphate" at the end of June last year after his fighters captured the Iraqi city of Mosul, asking all Muslims around the world to swear allegiance to him.
Signup to our newsletter and follow us on Facebook and Twitter!
A jihadist group in Algeria, another in Egypt's restive Sinai Peninsula, and one in Lebanon immediately pledged their allegiance to the new chief, followed over the next weeks and months by 18 other movements including Boko Haram in Nigeria -- taking the total so far to 21.
Ten other groups have voiced their support for IS, without pledging formal allegiance, IntelCenter said.
These 31 groups are very different in size and importance -- some meticulously structured with hundreds and even thousands of fighters, others barely existing or break-aways from known jihadist movements, experts say.