Illinois does not allow same-sex marriage - though advocates pushing for a law say the federal ruling adds urgency to their cause.
That's because of the approximately 1,100 federal benefits that are granted only to people who are married.
And civil unions - which are legal in Illinois - do not count.The effect of the Supreme Court's decisions is more complex when it comes to gay and lesbian couples who married in states like Iowa where it's legal, but who live in Illinois.
Christopher Clark is an attorney for Lambda Legal, a gay rights group. He says these couples will receive some of the federal benefits of marriage, but not others.
"I think we're going to need some clarification and probably the Obama administration and various federal agencies as to how they're going to interpret their practices going forward.”
Clark says given that President Barack Obama supports gay marriage, he's hopeful the administration will use a broad definition.