Multi-state child custody cases are governed by a law called the Uniform Child Custody Jurisdiction and Enforcement Act (UCCJEA).
According to the UCCJEA, any litigation over child custody should take place in the child’s home state. The child’s home state is the state where the child has lived with a parent for the six consecutive months prior to filing the action.
In the event the child has not lived in any state for at least six months, the courts in the state that has “significant connections” with the child and at least one parent, and a state in which there is substantial evidence concerning the child’s care, are in charge of the custody matters. If more than one state could qualify, the courts of those states should communicate in order to determine which state has the most significant connections to the child.
Once a state has determined custody, that state keeps jurisdiction over custody matters, unless one of two things happens – either a court in that state determines that the child and parent do not have a significant connection with the state and there’s no evidence available in the state; or a court of any state determines that the child and both parents don’t reside in the state any longer.
For an example, John and Jane got divorced in Wisconsin. Wisconsin courts decided Jane should be allowed primary custody. John later moved to Illinois and Jane moved to Florida with the children. John decides to fight Jane for primary custody. In that situation, Wisconsin would have to relinquish jurisdiction of the custody matter to Florida, where the children currently live.