Gay couples across Illinois are already making plans for weddings next summer.
The General Assembly has given final approval to a bill making Illinois the 15th state to legalize same-sex marriage.
Governor Pat Quinn says he will sign it into law.
During nearly three hours of debate Tuesday, opponents argued that the bill takes away religious freedom from people who oppose homosexuality, and will be harmful to children.
But supporters say gay couples and their families deserve the same protection that other married couples receive.
Once Quinn signs the bill, it will take effect next June 1st.