Kelso, MO has a population of 585 and is the 18,587th largest city in the United States. The population density is 1,845 per sq mi which is 2035% higher than the Missouri average and 1936% higher than the national average. The median age in Kelso is 31 which is approximately 20% lower than the Missouri average of 38. In Kelso, 68% of the population over 15 years of age are married, 95% speak English and 5% speak Spanish. 85% of Kelso residents were born in Missouri, 11% were born out of state, 0% were born outside of the United States and 4% were foreign born.