I want to marry my girlfriend so she can finally become a legal resident of the U.S. I am a U.S. citizen and she has been living in the States with "no status". We are both college students and we are both dependent on our parents until we graduate in May 2010. We were told we need a co-sponsor in order to be able to fix her situation. What are the requirements of that co-sponsor? I understand he/she has to make over $18,000, but does the co-sponsor have to be related to me? Is the co-sponsor required to do anything other than provide his signature, taxes and etc.?
A joint sponsor on the I-864 affidavit of support need not be related to you. You should review the instructions to the form carefully to determine what the co-sponsor is agreeing to.
It is unclear from your question whether your girlfriend entered the US legally of illegally. If she did not enter legally, she can not become a PR simply by marrying a US citizen without requesting certain waivers. In this regard, we suggest you contact a reputable immigration attorney.
If she entered legally, but is out of status, then a co-sponsor, who can prove that they earn more than $18,000 per year or have assets which exceed this amount, can sign as a co-sponsor. This joint sponsor does not need to be related to either of you, but will represent to the government that they will support your girlfriend financially.