Us Government--postal Service, Mt Morris Mount Morris, IL 61054 Phone : (815) 734-6518 Business Category Government Offices-Federal Government Offices & Public Schools Post Office - Mount Morris 21 W Main St Mount Morris, IL 61054 Phone : (815) 734-6518 Business Category Post Offices Toll-Free           (800) ASK-USPS Fax           (815) 734-9012