Illinois Population 2018
The population of Illinois in 2018 is estimated at 12.77 million. The 2015 Census estimates put the population at 12,859,995, which was a decrease from the 2014 numbers.
Illinois is one of only 7 states that has a negative growth rate in 2016. At -0.17% per year, it is ahead of only West Virginia. Between 2000 and 2010, the population of Illinois grew by a mere 3.3%, compared to the national average US population growth of 9.7%.
The 2016 population makes Illinois the fifth largest state in the USA based on population.
Chicago, Largest City in Illinois
Most of the Illinois population is based in the North East of the state. Chicago, home to 2,720,546 people, remains the largest city in Illinois. It dwarfs the state's other cities. The next largest is Aurora, with 200,661 people.
This marks one of Illinois' defining features -- although it has a large urban population, it is spread through a number of smaller cities. Including Chicago, there are twelve cities with more than 75,000 people.
Many of these smaller cities make up a part of the Chicago Metropolitan Area (prosaically also known as Chicagoland), which holds between 8.3 and 9.8 million people, depending on how you classify its boundaries.
Cook County is the largest county in Illinois, housing 5,238,216 people. The next largest county is neighboring Dupage, with 933,736 people. Almost half of the Illinois population can be found in just those two counties.
Illinois Population History
Illinois was included in the Northwest Territory established in 1787 and then in Indiana Territory (1800). Illinois Territory was established in 1809, and included virtually all of present-day Wisconsin and portions of Minnesota and the Upper Peninsula of Michigan. Illinois was admitted as a State on December 3, 1818 with essentially its present boundaries.
In 1790 the Northwest Territory had no census coverage. The population shown for 1800 is the total of two counties and one community in present-day Illinois, at that time part of Indiana Territory. Knox County, Indiana Territory, also included some population in what is now Illinois. In 1810, the returns for the two counties of Illinois Territory included some settlements in present-day Wisconsin. The northern part of the State was not fully covered by the census until 1830.