If I'm 18 and I plan on getting married with my 21 year old boyfriend, he is illegal and i am a citizen.Can my mother do anything to stop the marriage

If you are already the age of consent at 18, there does not appear to be anything that your mother can do to stop the marriage legally. Of course, she can threaten to report your boyfriend to ICE, but he would not be a high priority unless he has other unfavorable factors since there are approximately 11,000,000 undocumented individuals in this country. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.