In Illinois, the "date of separation" ISN"T the physical separation of the parties, nor is it defined merely by the filing of the Petition. While judgment was "executed" in just 2 weeks after filing, it is still possible that the actual "date of separation" was in excess of 6 months. Also in Illinois, if Judgment is entered by Agreement, BOTH parties have to execute a stipulation and waiver indicating the parties have been living "separate and apart" for a period in excess of 6 months and...
Your husband can file for divorce in any county he "resides", but no, he can't obtain a Judgment against you "behind your back". Due Process requires that the defendant in ANY action receive formal service and notice of the proceeding. Be careful about support--you may have a hard time getting him to contribute to the marital expenses and without legal action pending, have very little remedy to force him to contribute.
The first step is to contact your lender and see if something can be worked out through them with respects to refinancing, restructuring, or converting the existing mortgage. If they won't renegotiate the mortgage note, try to do a short sale. You may not get what you think you should from the equity, but you'll be out from under the mortgage and avoid having a foreclosure on your credit. If you and your husband are already separated, file for divorce, then consolidate the foreclosure...