The governent believed the youths were killed and incinerated.
The attorney general's office says the number of bodies found from October to May could be more, because it is counting only those instances in which its mass grave specialists get involved.
Iguala is a municipality of 120,000 people 200 kilometers (160 miles) south of Mexico City. A confrontation between students and police resulted in six deaths and the disappearance of 43 students. The search for the students turned up many mass graves.
The information was released because of an Associated Press freedom of information request.