Quincy is in the west central part of the state, on the Mississippi river.
The presumptive democratic presidential nominee pitched in on Saturday and helped fill sandbags. Obama said since he's been in public office he has not seen "this kind of devastation."
Governor Rod Blagojevich has declared parts of Illinois disaster areas.
Senator Obama said he's very concerned for his state and also for its neighbors across the river.
"Obviously, I spent a lot of time in Iowa. So I've grown attached to the people there. When you spend time in Cedar Rapids, you've got some of the most wonderful people in the country," said Obama.
The governor activated 200 National Guard soldiers to help with the sandbagging along the river.