There's still a lot of Polish immigrants around in Chicago and it seems pretty obvious to me that anyone speaking Polish at home nowadays would not be descended from the "old" turn of the 20th century Polish American population.
How these post-WWII Poles vote - I don't know.
Of the 65 places with more than 1000 persons that speak some Polish at home, 38 are in Illinois.
The question asked by the ACS is about whether a person speaks some Polish at home. The instructions say that this is more than just a few phrases or slang terms. But it doesn't mean exclusively Polish.
No but fluency in Polish would suggest in most cases relatively descended from recent immigration if not necessarily "off the boat."
Contrast the number of Polish speakers in the Chicago area as compared to say Detroit or Buffalo where the Polish American population is nearly all descended from the Ellis Island wave of immigration.
Speaking some Polish at home does not require fluency.
24.8% of Polish speakers reside in Cook County, but only 18% of those in Chicago. 2.84% of Cook County residents speak some Polish at home.
The only counties close are Hartford, CT 2.24%, Bergen, NJ 1.97%, and DuPage, IL 1.93%.
As you drop off on the concentration towards 0.5% you begin picking up other suburban counties of Chicago, such as McHenry, Will, and Lake, but extending out to Putnam and Kane.
You have counties in Connecticut, including Tolland and Middlesex, along with Hampden, MA.
You have almost every county in New Jersey, slightly more concentrated in Bergen, Passaic, and and Union, but spreading out into Hunterdon, and Cape May.
IN New York, the highest concentrations are in Queens and Staten Island, but extending outward to Suffolk, Orange, Dutchess, and Fairfield, CT.
Monroe, Pike, and Carbon, PA all in the northeastern corner.
Higher concentration and numbers in Macomb, then Oakland, and finally Wayne. I wouldn't be surprised if the numbers in Macomb now exceed those in Hamtramck.
At a state level, Florida is 5th in numbers, and Texas, Arizona, and California are all in top 15 with 1% of the total.
Either those totally assimilated Polish Americans continue to speak some Polish at home in their tract homes in El Rancho Polonia, or there are lots of "real Polish" living in the suburbs.