Pittsfield, IL has a population of 4,604 and is the 6,832nd largest city in the United States. The population density is 968 per sq mi which is 336% higher than the Illinois average and 969% higher than the national average. The median age in Pittsfield is 42 which is approximately 13% higher than the Illinois average of 37. In Pittsfield, 58% of the population over 15 years of age are married, 98% speak English and 1% speak Spanish. 81% of Pittsfield residents were born in Illinois, 18% were born out of state, 0% were born outside of the United States and 1% were foreign born.