That being said, we don't typically see that sort of flooding along the river, but that doesn't mean it's not possible, nor does it mean that it's not likely.
Your lender will require special "flood" insurance in order to make a loan on a property in a flood plain, and you should probably talk to your Realtor, and perhaps some other people in the neighborhood, who have lived through flooding in the area, as to what it means "practically". Do residents merely get some seepage in their basements, or do they get standing water. Do their yards flood? Does the typical flooding extend into the houses... (feet of standing water?), is there current flooding damage to the structure of the house?
And once all of those questions have been answered, are you willing to live with the potential? There are plenty of people, like Cathi, who live in those homes in Franklin Park, Des Plaines, along the Des Plaines river, and in the flood plain and they seem to be managing just fine.
It shouldn't be a deal killer. You will want to talk to your insurance company as they will be taking a look at this anyway.
I live in Franklin Park and don't recall any major issues with flooding near Silver Creek. You can contact the Village Hall and talk with them as well at 9500 W. Belmont, 847-671-4800.
If you are concerned that your home will actually flood, besides the disclosures provided by the seller, I would talk with some long time neighbors and ask them if their homes have flooded. With the big storm we had in August, you should be able to get a sense for what might occur in the immediate area by talking to others.