Post Offices in Mount Vernon, Illinois, United States SearchSearch SearchSearch View: Grid 1View: Grid 2View: Grid 3View: Grid 4View: Grid 5View: List Mount Vernon Post Office No Reviews Favorite Fax: (651) 994-3232Phone: (618) 242-0640Retail Hours Mount Vernon Carrier Annex Post Office No Reviews Favorite Phone: (618) 242-0700Retail Hours