The mean population center of Illinois is relatively close to Chicago:

[B]ased on new data from the U.S. Census, the true center point of Illinois’ population is about 70 miles southwest of Chicago’s bustling Magnificent Mile.

Situated in a corn field east of the intersection of U.S. Route 47 and Illinois Route 113 in Grundy County is the point referred to by the census as the Mean Center of Population for Illinois…

The center point can tell a lot about a state.

It can help explain why Illinois has a state government controlled largely by Chicago politicians.

It can help explain how money gets distributed around the state. It can help explain why some issues — say, gun control — can pit rural interests against urban interests.

“Somewhere close to half the population of the state is within 40 miles of the Loop,” Illinois State University geography professor Mike Sublett said.

This is not too surprising: by far, Chicago is the largest city in the state and the population of the Chicago metropolitan region (2009 estimate of the Illinois portion only – not counting Wisconsin and Indiana populations) is just under 8 million while Illinois’ total population is just over 12.8 million (2010 figures).

But the value of such a measure seems to be not exactly where this mean is located but rather how this population mean has shifted over time. The article goes on to note how the population mean wasn’t always so close to Chicago:

In the 1840s, the center point was located east of Springfield, relatively close to Illinois’ geographical center point in the Logan County community of Chestnut.

But, as Chicago began to grow as an urban center, the population center point began its northward trek along a line nearly mirroring what would become Interstate 55.

The 1880 center of the state’s population was on the south side of Bloomington, near U.S. Route 150 south of where State Farm Insurance Cos. has its Illinois regional office complex.

In 1910, the center moved out of McLean County for the first time in 50 years. The new center was in a farm field just a few miles southeast of Pontiac.

The only time it took a break from its northeasterly trek until recently was in 1940, when the center — then located in Livingston County — briefly moved southward…

The northern movement of the center point also has stalled in recent decades. The 2010 center point near south of Morris in Grundy County is somewhat south of the 2000 and 1990 population centers, located just a few miles away.

Sublett attributes the stall to the rapid growth of Chicago’s western suburbs and the loss of population within the state’s largest city.

“The center point has kind of stagnated. It has just been migrating around Grundy County,” Sublett said.

As I’ve written before regarding the US population mean (see here), the population mean measure seems to make the most sense when placed in a historical context so that people can get a quick look at larger population and migration trends.

I wonder how many Chicago area residents know that the bulk of the state’s early population lived in the central and southern portions of the state and it wasn’t really until the 1840s and 1850s that the population of northeastern Illinois really began to grow and tilt the balance of power in the state.