Monroe Street, Suite 104 Marion, IL 62959 Phone: 618-998-2142 Fax: 618-997-2541 Email: treasurer@williamsoncountyil.gov Office Hours: Monday-Friday, 8:00 a.m. - 4:00 p.m. Contact Us Property Tax Payment Dates 1st Installment: October 23, 2023 2nd Installment: November 30, 2023.