Yes, I see what you're saying. The instructions do not seem to address your particular situation. However, I would tend to think the same applies. Either treat them both the same, or file separately. Assuming the taxpayer has no IL source income, your situation would be fairly straightforward. File one IL return only under the spouse's name. Taxpayer wouldn't even need to file a IL return. If taxpayer has IL source income, then two IL returns would be required. Either scenario would require two separate files in ProSeries. First prepare Federal return like normal, designating income correctly between spouses. Second, "Save As" under a new file name, and simply swap names on the General Information sheet, then choose MFS for IL.