Michigan and Illinois's population growth of the 1990's vs other recent decades:

[hopper]

My question is why did Michigan and Illinois gain a lot more people in the 1990's than other recent decades?

Illinois gained 1 million new people(well 988,700) in the decade of the 1990's from 11.4 million to 12.4 million. In the 1980 census Illinois grew by 312,600 people and in the 1990 Census it only grew by 4,100 people a net increase of 0% increase population wise. In the 2010 Census the state gained 411,400 people.

Michigan gained 36,300 people in the 1990 Census and in the 2000 Census gained 643,100 more people. In the last 2010 Census and 2012 Census the state has lost a combined 55,100 people.

[muon2]

Immigration growth fueled the increase in IL after 1990. Since 1990 foreign-born population growth accounts for half the the total growth in each of the last two decades. With foreign-born immigrants come native-born children and they make up a lot of the rest of the growth.

[Brittain33]

May indicate an undercount in 1990. I remember that when the 2000 census came out, the overall increase and that in several states was surprisingly high.

[minionofmidas]

May indicate an undercount in 1990. I remember that when the 2000 census came out, the overall increase and that in several states was surprisingly high.

The 1990 census' flawedness (by high first world regular censustaking country standards) is notorious, and was known well before 2000 and recognized by the Bureau itself.

Wouldn't go so far as to try and explain this issue on that alone, though.

[hopper]

I just corrected that Illinois grew by 411,400 people in the 2010 Census. I had put the 2000 Census instead to start the topic. My mistake.