I keep getting calls from this number, too, but no caller ID or messages. Reverse directories give no info, so I googled the number and got the Cook County (Chicago, IL) Government Administrative Offices. I live in Chicago but have no idea why they'd be calling ... or how they got my cell number.
This is the Cook County Court Clerk. They use this line to call people to let them know the archived case files they ordered are in. The problem is that the orders are hand-written, as are the contact numbers. It is very likely that the clerk is simply attempting to call an attorney or other legal worker who has really illegible handwriting (and are mis-reading a number or two).
Either that or it's really bored clerks prank calling. If you didn't order a file from Cook County (or have other dealings with the court clerks), just ignore it.
Chicagoans often call Minneapolitans because combine a crazed court clerk with the 6 and 3 button being so close to each other results in calls to Minneapolis cell phones, apparently she wanted Lex who was working on their IT system or something