Voters seemed evenly divided over Obama's signature health-care law, the Affordable Care Act, and whether it should be repealed.
Retired railroad engineer William Jaworski, 70, said he is a Democrat but voted for Romney partly because of the law, often referred to as Obamacare.
"The Obamacare makes me nervous," said Jaworski, of Elk Grove Village. "I don't think it would affect me personally because I have supplemental insurance, but I don't like it all where they're going to try and force the Catholic church and the Catholic hospitals and Catholic institutions to (supply) contraceptives and things that are against the churches teaching."
A majority of voters agreed with Obama on two social issues he has advocated: legal recognition for gay marriage and giving illegal immigrants a way to apply for permanent residency.
"I'm shocked that a sitting president would come out and say he supports gay marriage," said Linda Sherwood, 50, a house remodeler from Springfield who voted for Obama. "I was hoping he was going that way ... He never ceases to amaze me."
Obama won 74 percent of the vote in Cook County overall, including Chicago. He also squeaked by in traditionally Republican DuPage County, which broke a streak of voting for the GOP presidential candidate when it backed Obama in 2008, and won Kane, Lake and Will counties. Romney won most of less populated counties in southern and western Illinois.
Standing before a jubilant crowd at McCormick Place convention center in Chicago, Obama said that while the road has been hard, the country has "fought our way back" and that the best is yet to come.