Smithville, MO has a population of 8,791 and is the 4,300th largest city in the United States. The population density is 568 per sq mi which is 552% higher than the Missouri average and 527% higher than the national average. The median age in Smithville is 38 which is approximately equal to the Missouri average of 38. In Smithville, 69% of the population over 15 years of age are married, 96% speak English and 2% speak Spanish. 58% of Smithville residents were born in Missouri, 39% were born out of state, 0% were born outside of the United States and 2% were foreign born.