U S Government--post Offices, Williamson Chariton, IA 50049 Phone : (641) 862-3812 Business Category Post Offices Government Offices & Public Schools Post Office - Williamson 103 W South Ave Williamson, IA 50272 Phone : (641) 862-3812 Post Office - Williamson Business Category Post Offices Toll-Free           (800) ASK-USPS