Can a US citizen legally marry an illegal immigrant?
hell no why would they want too
Yes.May be the immigrant could file Form I-601 provided the marriage is in good faith.Ample proofs and support documents are required for Form I-601 filing.
In the United States some of the inadmissible non-immigrant applicants and aliens who are not eligible to be admitted as an immigrant or adjust status in US must file Form I-601 in order to seek a waiver of certain grounds of inadmissibility. They must submit all 11 pages of the INS forms. The Filing Fee is $585.