Office Locations TRI-COR Corporate Headquarters 4600 Forbes Blvd., Suite 205 Lanham, Md 20706 (301) 731-6140 Field Offices O'Fallon, IL 5 Eagle Center, Suite 8 O'Fallon, IL 62269 (618) 632-9804 St. Louis, MO 462 N. Taylor Ave. , Suite 203 St. Louis, MO 63108 (314) 531-2433 San Antonio, TX 2941 Mossrock, Suite 105 San Antonio, TX 78230 (210) 979-0552