Fairfax, MO has a population of 703 and is the 17,455th largest city in the United States. The population density is 1,510 per sq mi which is 1648% higher than the Missouri average and 1567% higher than the national average. The median age in Fairfax is 43 which is approximately 13% higher than the Missouri average of 38. In Fairfax, 66% of the population over 15 years of age are married, 98% speak English and 1% speak Spanish. 74% of Fairfax residents were born in Missouri, 24% were born out of state, 0% were born outside of the United States and 1% were foreign born.