Fort Belvoir, VA has a population of 8,204 and is the 4,609th largest city in the United States. The population density is 934 per sq mi which is 388% higher than the Virginia average and 931% higher than the national average. The median age in Fort Belvoir is 22 which is approximately 42% lower than the Virginia average of 38. In Fort Belvoir, 73% of the population over 15 years of age are married, 88% speak English and 8% speak Spanish. 13% of Fort Belvoir residents were born in Virginia, 76% were born out of state, 7% were born outside of the United States and 5% were foreign born.