40 ILCS 5/10-106: Employees with county while on leave from district.

If an employee on leave of absence from the service of the district is employed by the county, the board shall cause deductions to be made from his salary on the same basis as if he were employed by the district. The sums so deducted shall be placed in the fund to be used for the benefit of the employee.

Contributions on behalf of the employee shall be made by the forest preserve district, and placed in the fund on the same basis as if the service for the county had been rendered the district. The employee shall have the same rights in the fund while such service is being rendered for the county and after the service is terminated as if the service was rendered for the district.