the law does not use the term domestic partnership. the city of chicago does for employee benefits to family. there is an appellate court case of that. some private companies use the term for the same purpose.
in order to have a valid civil union, you must comply with the civil union law. just living together does not do it. if you do a civil union now, you may convert it to a marriage under the new law. but you must then comply with that law.
as on next june, you could get married in illinois.
To be able to have legal rights as a partnership you need to have gone through a civil union as provided by the Clerk of the Court. This can later be turned into a marriage after the new law goes into effect in June (or sooner!) The term domestic partner is really just a term that talks about various insurance plans and who the employer has agreed can be eligible for coverage. You will need to ask HR at your boyfriend's employer if they have domestic partnership benefits or is a civil union or marriage is required. You can also inquire then about children and how they would or could he covered depending on your legal relationship to your partner.
This will all be so much more straight forward once the marriage equality law becomes effective.
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