Illinois' population loss was the worst in the country on a numerical basis, and on a percentage basis it was second from the bottom, with only West Virginia faring worse. Number one was Texas with an increase of just under 400,000 residents.
Wyoming saw the largest percentage decline.
IL was one of eight states to lose population, and had the largest numeric decline, the Census Bureau said.
As for why the decline is happening, Harger said it could be linked to a declining birth rate for the state, a drop in domestic migration - meaning people coming to IL from other states - and a "leveling off" of foreign migration.
That's roughly double the net migration figure from the previous year, which was -4,000.
"A lot of states have witnessed similar issues and come back from them", Harger said, referring to Pennsylvania, which he says has seen a population increase of about 103,000 since 2010.More news: This Is What Caused the Massive Power Outage at the Atlanta Airport
More news: Indian shares advance led by banks after Gujarat exit poll results
More news: Google finally gives more Android phones their own Assistant
This marks the fourth consecutive year of population decline in IL. However, roughly 8,300 more people left Wyoming than moved into the state.
Meanwhile, Pennsylvania saw modest population growth of 18,400 people over the same time.
The migration figure is based on two factors, domestic and global.
Migration from other states and countries accounts for the majority of the population increase, according to the data. That and a net gain of 6,836 global migrants made up for a net loss of 2,724 people moving to other states, according to the estimates.
That combined with the natural change result adds up to the 36,000 population increase. But Connecticut attracted some 17,000 people from other countries, a little more than a third of the number for MA.