Potomac, IL has a population of 675 and is the 17,692nd largest city in the United States. The population density is 1,383 per sq mi which is 522% higher than the Illinois average and 1426% higher than the national average. The median age in Potomac is 33 which is approximately 12% lower than the Illinois average of 37. In Potomac, 53% of the population over 15 years of age are married, 99% speak English and 1% speak Spanish. 84% of Potomac residents were born in Illinois, 15% were born out of state, 1% were born outside of the United States and 0% were foreign born.