Union County Treasurer Share: Government Union County Treasurer Visit Website 233 W. 6th St. Marysville, OH 43040 (937) 645-3035 (937) 645-3094 (fax) www.co.union.oh.us/treasurer Hours: Monday - Friday 8:30 AM - 4:30 PM (Closed for all County Holidays) About About County Elected Official - Union County Treasurer