U S Government Offices--post Office, Saint Xavier Yellowtail, MT 59035 Phone : (406) 666-9171 Business Category Government Offices-Federal Post Offices Government Offices & Public Schools Post Office - Saint Xavier 108 Fort Smith Ave Saint Xavier, MT 59075 Phone : (406) 666-9171 Post Office - Saint Xavier Business Category Post Offices Toll-Free           (800) ASK-USPS