If you meet certain requirements, you may become a US citizen either at birth or after birth. Use this form to apply for US citizenship.Be at least 18 years old at the time of filing Form N-400, Application for Naturalization. You should complete the worksheet before filling out Form N-400. Our online service provides step-by-step Form I-130 instructions so that you can fill out the petition in just a few minutes. Processes all naturalization applications and provides the Court with a list of the candidates selected to be naturalized in the Federal Court. You'll have to fill out form N-400, the Application for Naturalization within the U.S. Citizenship and Immigration Services (USCIS). Form I-130: Petition for Alien Relative is the first form you must file to start the marriage-based green card application process. Adjustment of status allows U.S. citizens to apply for the lawful permanent residence of their immediate family members who are currently in the United States. Utah; Vermont; Washington; West Virginia; Wisconsin; Wyoming.