820 ILCS 115/3) (from Ch. 48, par. 39m‑3)
Sec. 3. Every employer shall be required, at least semi‑monthly, to pay every employee all wages earned during the semi‑monthly pay period. Wages of executive, administrative and professional employees, as defined in the Federal Fair Labor Standards Act of 1939, may be paid once a month. Commissions may be paid once a month. At the request of a person employed by an employment or labor placement agency which, in the ordinary course of business, makes daily wage payments to employees, the agency shall hold the daily wages and make either weekly or semi‑monthly payments. Upon the written request of the employee, the wage shall be paid in a single check representing the wages earned during the period, either weekly or semi‑monthly, designated by the employee in accordance with Section 4 of this Act. Employment and labor placement agencies that make daily wage payments shall provide written notification to all daily wage payment employees of the right to request weekly or semi‑monthly checks. The employer may provide this notice by conspicuously posting the notice at the location where the wages are received by the daily wage employees.
(Source: P.A. 89‑364, eff. 8‑18‑95.)
(820 ILCS 115/4) (from Ch. 48, par. 39m‑4)
Sec. 4. All wages earned by any employee during a semi‑monthly or bi‑weekly pay period shall be paid to such employee not later than 13 days after the end of the pay period in which such wages were earned. All wages earned by any employee during a weekly pay period shall be paid not later than 7 days after the end of the weekly pay period in which the wages were earned. All wages paid on a daily basis shall be paid insofar as possible on the same day as the wages were earned, or not later in any event than 24 hours after the day on which the wages were earned. Wages of executive, administrative and professional employees, as defined in the Federal Fair Labor Standards Act of 1938, may be paid on or before 21 calendar days after the period during which they are earned.
The terms of this Section shall not apply, if there exists a valid collective bargaining agreement which provides for a different date or for different arrangements for the payment of wages.
http://www.ilga.gov/legislation/ilcs/ilcs3.asp?ActID=2402&ChapAct=820 ILCS 115/&ChapterID=68&ChapterName=EMPLOYMENT&ActName=Illinois+Wage+Payment+and+Collection+Act%2E