Stillman Valley, IL has a population of 1,075 and is the 14,690th largest city in the United States. The population density is 1,980 per sq mi which is 791% higher than the Illinois average and 2086% higher than the national average. The median age in Stillman Valley is 36 which is approximately 3% lower than the Illinois average of 37. In Stillman Valley, 68% of the population over 15 years of age are married, 99% speak English and 0% speak Spanish. 86% of Stillman Valley residents were born in Illinois, 14% were born out of state, 0% were born outside of the United States and 0% were foreign born.