Williamson, IL has a population of 233 and is the 23,752nd largest city in the United States. The population density is 155 per sq mi which is 30% lower than the Illinois average and 71% higher than the national average. The median age in Williamson is 35 which is approximately 7% lower than the Illinois average of 37. In Williamson, 68% of the population over 15 years of age are married, 99% speak English and 0% speak Spanish. 81% of Williamson residents were born in Illinois, 18% were born out of state, 0% were born outside of the United States and 1% were foreign born.