40 ILCS 5/12-177: Employee accounts.

The amounts contributed by employees for service annuity and spouse's service annuity shall be credited to this account; also all amounts contributed by the employer in lieu of deductions from salary in cases of ordinary or duty disability.

An individual account shall be kept with each employee. As contributions by or on behalf of the employee are made, each such account shall be credited with the amounts thereof. At least once each year each account shall be credited with regular interest.