Elon,
Dude, I know you're a lot smarter than I am, but there's already an existing train from O'Hare to downtown Chicago that travels about half that speed and gets you there in about 30 minutes for $2, which is perfectly adequate for most non-billionaires.
Instead of building a faster, but redundant train line for one sole use case, why not build hyperloops from downtown Chicago to the downtown areas of regional cities like Milwaukee, Des Moines, Indianapolis and St. Louis, which would have a multitude of use cases and be an absolute boon to the regional economy?