Walnut Grove, MO has a population of 640 and is the 18,036th largest city in the United States. The population density is 1,031 per sq mi which is 1094% higher than the Missouri average and 1038% higher than the national average. The median age in Walnut Grove is 37 which is approximately 2% lower than the Missouri average of 38. In Walnut Grove, 66% of the population over 15 years of age are married, 98% speak English and 1% speak Spanish. 67% of Walnut Grove residents were born in Missouri, 30% were born out of state, 0% were born outside of the United States and 2% were foreign born.