An illegitimate child is one born to parents who are unmarried at the time of his birth. In the past, such a child was legally known as a "filius nullius" or "child of no one." Even subsequent marriage of the child's parents is insufficient to render him legitimate. Likewise, a child born to parents of a bigamous marriage is considered illegitimate. Children of a later-annulled marriage were once considered illegitimate, but state law has changed to render them legitimate. In recent years, the law has largely abandoned the term "illegitimate" in favor of the term "born out-of-wedlock" to describe such children.
Traditionally, under common law, an illegitimate child was not a legal child to either of his parents. The law valued family relationships and considered family to be established only by marriage. An illegitimate child had no right to parental support and no right to inherit through either parent. He was effectively on his own. However, an illegitimate child's descendants could still inherit through him.
By the 20th century, although many states had given illegitimate children the right to inherit through one or both of their parents, some states still limited the legal rights of an illegitimate child. In the 1968 case of Levy v. Louisiana, the U.S. Supreme Court ruled that state laws that denied illegitimate children rights based on their illegitimacy were unconstitutional under the Equal Protection Clause. In the 1977 case of Trimble v. Gordon, the Supreme Court struck down a state law provision that denied an illegitimate child the right to inherit from her father unless the father's will stipulated the inheritance. These cases, among others, established the right of an illegitimate child to some form of legal inheritance.
At this point, all U.S. states have given an illegitimate child the right to inherit from his mother. However, paternal inheritance rights remain inconsistent. Most states do not automatically consider an illegitimate child to be the legal child of his father. These states allow the child to present evidence of his paternity although many of these states often demand that paternity be proven during the father's lifetime. Acceptable forms of evidence in various states include evidence of subsequent marriage to the mother or the father's legal acknowledgment of paternity. Some states will also allow DNA testing as proof, even after the father's death.