The Illinois Department of Revenue has finally issued guidance saying that couples in same-sex civil unions can file as married on their state tax returns.
Illinois passed a law in June that allows same-sex civil unions. At the time, the Illinois Department of Revenue had said that couples in same-sex civil unions would NOT be able to file as married on their state returns. Later, the Department retracted that decision and said it was “reviewing” the situation. On Monday, the Department finally issued a ruling saying couples in same-sex civil unions can file as married. You can read more in this Chicago Tribune article.
This puts same-sex couples in Illinois into the same boat as gay couples in marriages/civil unions/domestic partnerships in other states (such as Iowa). Because of the federal Defense of Marriage Act (DOMA), same-sex unions and marriages are not recognized for federal purposes, so gay couples have to file their federal returns as either single or head of household, and then create a mock joint return to prepare the state return.