The executions were carried out over accusations of sorcery, sodomy, adultery, banditry, joining and cooperating with rival militant groups, cooperating with US-led coalition fighting ISIL and cooperating with Syrian army forces, the so-called Syrian Observatory of Human Rights reported.
The UK-based group said that the executions - mostly beheadings - took place between July 29 and August 29, Al Jazeera reported on Sunday.
At least 32 civilians, including two women, were among the executed, the Observatory said. There were also 11 fighters from different militant groups and nine members of Syrian army among them, it said.
Since the declaration of its so-called "Islamic Caliphate" in June last year, ISIL has executed 182 of its own members who had been captured trying to flee the group and return home, the UK-based Observatory said.
The Observatory said that over the past year, ISIL executed 1,841 civilians, including 76 children and 95 women, by shooting, beheading, stoning, throwing off from high buildings and burning to death.
The figures cannot independently be verified.
ISIL has taken vast parts of Iraq and Syria and declared a state in territory under its control. Since then, thousands of foreign extremists from all over the world arrived in Syria and Iraq to fight with the group.
Several reports had emerged of European fighters wanting to return home but were afraid for their lives.
ISIL has released dozens of videos of executions of captured enemy fighters, activists and journalists.
In 2014, it beheaded two US journalists, and one American and two British aid workers in attempts to put pressure on a US-led international coalition, which has been bombing its positions in Syria since September.