Approximately 85 percent of all immigrant families with children are mixed-status families, i.e. one parent is a legal or illegal immigrant with at least one child who is a U.S. citizen. According to a 2012 Applied Research Center report, "Shattered Families," there are 4.5 million American children in mixed-status families -- one parent is a U.S. citizen and the other an illegal immigrant.
Your mom may be an illegal immigrant for a variety of reasons, most likely because she either crossed U.S. borders into the United States without any legal immigration documents or she stayed beyond the time indicated by the visa stamp on her passport. If your mom and your dad did not take legal steps to obtain an immigration waiver, official permission from the U.S. government permitting her to live in the United States legally, your mom can be arrested and deported by the U.S. Immigration and Customs Enforcement (ICE) agency at any time.
Divorce and Custody
A custody dispute between a U.S. citizen and an illegal immigrant is conducted by family courts in the same manner as a custody dispute between two U.S. citizens. Courts generally award custody using a standard called the best interests of the child, trying to determine whether you would be better off if your parents have joint custody or one parent retains sole custody. A family court will not turn your mom over to ICE.
State Court Differences
Your mom's immigration status is usually considered as one item among many different factors in determining whether one or both parents should have custody of you. Each state also has its own set of laws. One court may decide that because your mom could be deported by ICE, your dad should have custody of you unless he is proven to be an unfit parent. Even if a court awards custody of you to your mom, she may still lose custody to your dad if ICE deports her. On the other hand, another court may give custody to your illegal immigrant mom and order your U.S. citizen dad to pay her alimony, child support and assist her in becoming a legal immigrant.
Ideally, your parents will agree on a custody arrangement they can both live with and your mom will remain in the United States. In 2011, the Obama administration announced a decision to focus on deporting illegal immigrants who have committed crimes instead of deporting illegal immigrants who are not a threat to public safety.