In which state do I file for custody?
As is explained in a law called the Uniform Child Custody Jurisdiction and Enforcement Act (UCCJEA), you can only file for custody in the “home state” of the child (but please also take a look at Are there exceptions to the “home state” rule?). The “home state” is the state where your child has most recently lived with a parent or a person acting as a parent for the past six consecutive months. If your child is less than six months old, then your child’s home state is the state where s/he has lived since birth. Leaving the state for a short period of time, such as going on vacation, does not change your child’s home state.
If you and your child recently moved to a new state, generally you cannot file for custody in that new state until you have lived there for at least six months. Until then, you or the other parent can start a custody action in the state where your child has most recently lived for at least six months.1 However, there are exceptions - please see Are there exceptions to the “home state” rule?
1 See NJSA § 2A:34-65