Zip codes for the Fort Smith (AR-OK) metropolitan area (as defined by the United Fort Chaffee, , Sebastian County, Arkansas - AR, Fort Smith. FIPS code, GNIS feature ID, Interstate Highways · I, I, I Other major highways, US 64, US 71, US Website, City of Fort Smith. Fort Smith is the second-largest city in Arkansas and one of the two county seats of Sebastian Zip codes[show]. , , , Fort Smith lies on the Arkansas-Oklahoma state border, situated at the junction of the Arkansas and Poteau Rivers, also known as Belle Point. Dancers perform at many local events. It established the Fort Chaffee Military Reservation east of the city. The racial makeup of the city was The US founded Fort Smith in as a military post. John Rogers, an Army sutler and land speculator, bought up former government-owned lands at this site and promoted growth of the new civilian town of Fort Smith. He was instrumental in achieving statehood for Oklahoma inafter Native American claims were extinguished by distribution of communal lands under the Zip code in fort smith arkansas Act and the breakup of tribal governments.