Thomson, IL has a population of 563 and is the 18,831st largest city in the United States. The population density is 235 per sq mi which is 6% higher than the Illinois average and 160% higher than the national average. The median age in Thomson is 42 which is approximately 13% higher than the Illinois average of 37. In Thomson, 66% of the population over 15 years of age are married, 98% speak English and 0% speak Spanish. 50% of Thomson residents were born in Illinois, 49% were born out of state, 0% were born outside of the United States and 1% were foreign born.