Ill COMP STAT § 5 : Illinois Statutes - Section 5

820 ILCS 115/5) (from Ch. 48, par. 39m‑5)
Sec. 5. Every employer shall pay the final compensation of separated employees in full, at the time of separation, if possible, but in no case later than the next regularly scheduled payday for such employee. Where such employee requests in writing that his final compensation be paid by check and mailed to him, the employer shall comply with this request.
Unless otherwise provided in a collective bargaining agreement, whenever a contract of employment or employment policy provides for paid vacations, and an employee resigns or is terminated without having taken all vacation time earned in accordance with such contract of employment or employment policy, the monetary equivalent of all earned vacation shall be paid to him or her as part of his or her final compensation at his or her final rate of pay and no employment contract or employment policy shall provide for forfeiture of earned vacation time upon separation.
(Source: P.A. 83‑199.)