Illinois Statutes Chapter 50. Local Government § 505/4. Payment of bills; penalty

§ 4. Any bill approved for payment pursuant to Section 3 shall be paid within 30 days after the date of approval. If payment is not made within such 30 day period, an interest penalty of 1% of any amount approved and unpaid shall be added for each month or fraction thereof after the expiration of such 30 day period, until final payment is made.