If Chicago Would Succeed from Illinois

As you may have heard there is a movement afoot to have Chicago succeed from Illinois. I am not here to justify whether this is a good idea or not but it does have an interesting result - the rest of Illinois would become a swing state.

Now it is not clear what people mean exactly when they say Chicago would succeed from Illinois. I can think of three ways this could go:

1. The city of Chicago would succeed but all other parts of Cook County would stay in Illinois.
2. All of Cook County would succeed from Illinois. This means Illinois would go from 102 counties to 101 counties. (This is assuming no townships succeed from Cook County)
3. Cook County and all 5 collar counties (DuPage, Kane, Lake, McHenry, and Will) would succeed. With this Illinois would go down from 102 to 96 counties.

My gut feeling says #3 is really unlikely just because there are many people in the suburbs who would rather stay in Illinois than leave together with Chicago. However, I am leaving in #3 for completeness. Below you would see the percentage of the Democrat candidate for president if Chicago (and its suburbs) broke off from Illinois:

	Illinois Today	#1 Illinois w/o Chicago	#2 Illinois w/o Cook Co	#3 Illinois w/o Cook and Collar Counties
2000	56.2%	49.6%	46.8%	47.8%
2004	55.2%	48.7%	45.4%	45.1%
2008	62.7%	56.9%	53.7%	51.9%
2012	58.6%	52.2%	48.3%	46.3%
2016	59.0%	52.0%	46.6%	40.3%

Sources: [1][2]
Note: for calculation of percentages I only considered votes for a Republican or Democrat and did not consider third party candidates.

As you can see in the table above once you take out Chicago the presidential elections since 2000 would have become very close for Illinois.

The chances of Chicago succeeding from Illinois is pretty slim. The last time a state was broken up is when West Virginia succeeded from Virginia in 1863. However even if this is more of a thought experiment than anything else it does make the point that in the end Democrats would probably benefit more than Republicans. This is a bit ironic because it is mostly Republicans in Illinois, not Democrats, pushing this issue. The Democrats would get 2 more presidential electoral votes and would have great chances to win the rest of Illinois. Even in the Senate the Democrats would probably get those 2 extra seats with Chicago as a state.