Illinois' Pontiac, Sheridan and Stateville prisons will have more guards on rotation.
The Departments of Corrections said most of the employees who had been working at the Dwight correctional center started their new jobs on Monday.
Gov. Pat Quinn closed Dwight, as well as the Tamm's super-max facility in southern Illinois, to save money.
Critics say it's a mistake to close prisons when they are already over crowded.
According to the DOC, only a small, clean-up crew is still working at Dwight.