It looks like they have sold securities/interests in the company to the public, but they are not a "public company."

https://www.sec.gov/info/smallbus/secg/formdguide.htm
https://en.wikipedia.org/wiki/Form_D

LLC can have owners, members, and managing members. Untangling these types of ownerships interests is generally not possible since they have no reason to disclose their inside operations to the public. Often times the only people who truly know the ownership interests are the owners themselves.

You might be able to find UCC Filings and recorded documents at the county recorder level in Chicago to uncover ownership interests; usually financing documents and their signature blocks will disclose the type of interests. For example, the loan might be in the name of "abc llc", and you find the companies who signed the docs are actually "def Inc." and "ghi inc" as members, or managing members (of abc llc), etc., etc.

You can throw tons of time at it....