Illinois State Law Illinois recognizes same-sex relationships under state law as follows: Same-Sex Marriage Illinois prohibits same-sex marriage.  A marriage between persons of the same sex legally entered into in another jurisdiction is generally recognized as a civil union in Illinois. Click here for more information. Civil Unions Unmarried persons of the same sex may establish a civil union in Illinois. A party to a civil union is generally entitled to the same legal obligations, responsibilities, protections, and benefits as are afforded or recognized to spouses under state law. A civil union or a substantially similar legal relationship (other than common law marriage), legally entered into in another jurisdiction, is generally recognized in Illinois as a civil union. Click here for more information.