Okay, Matt. I am going to take a few guesses here.
I am guessing that what you received was a notice from your ISP advising you of a subpoena issued to and received by your ISP, and that it is your ISP that is required to respond to the subpoena by producing the documents, records, etc. that have been requested. These records would include your name, address, telephone number, email address, and any other identifying information your ISP has (your account information). Your ISP is notifying you of this subpoena so that you have the chance to respond by filing a motion with the Court to quash the subpoena, preventing the release of your identifying information.
I am also guessing that, with this subpoena, there is no personal court appearance required of you, and that at this point in time your computer is not the subject of a discovery demand and will not be inspected. BUT without seeing exactly what you received, it is impossible for me to tell this for sure.
Subpoenas were issued by the Court, more than likely, so that the Plaintiff (Patrick Collins, Inc) will be able to complete service of process on you and the other John Does in the case. Courts can authorize this early discovery if good cause is shown, if there is no other way to identify the defendant(s) in an action.
You really need an attorney, though, Matt, and you should locate one soon to help you. An attorney may advise that you file a motion to quash the subpoena along with filing a motion to dismiss you from the suit, based on a variety of grounds (your Illinois residence, for one). There are deadlines for filing these motions that must be met, however. You do not want to miss any important deadline if timely filing can get you dismissed from this suit. Dismissal from this California suit stands to be only a temporary reprieve for you, however, as another suit can be, and probably would be, filed against you later.
BUT again, as I said, these are GUESSES I am making based on the limited amount of information provided by you in these posts. You really need to have an attorney in your area review your situation and ALL of the facts. This personal review by an attorney in your area is necessary to determine your best course of action.
I agree with eerelations that you are not in an enviable position right now. This is liable to be a very costly lesson in copyright law for you.