Five primary schools in Cavan and Monaghan have classes of 35 pupils or more.
Figures provided to Sinn Fein's Education Spokesperson showed 71 classes in the two counties have more than 30 students.
Across Ireland, there are 2,120 primary classes with 30 pupils or more in the last academic year.
36 of them are in Cavan, and 35 in Monaghan.
This figures were given to Sinn Fein TD Donnchadh Ó Laoghaire.
However further Department of Education figures show four schools in Monaghan and one in Cavan have classes with 35 pupils or more.
Edenmore National School has 39 students in one class, and 36 in another.
While St Tiarnach's in Clones has two classes of 36.
Scoil Eanna in Ballybay has a class of 38, and Scoil Rois in Carrickmacross has a class of 36.
Searcog NS in Shercock has a class of 35, the highest class size in the county.
The Department of Education says that from September 2022, there should be an average teacher-student ratio of 1 to 24.