If the mother consents can you take your child across state lines permanently without legal documentation or do you still need to go through the courts?

I assume you are unmarried. Generally in the United States, an unmarried mother has sole legal custody of her child automatically. An unmarried father must establish his paternity legally in court in order to gain parental rights. Once established he can petition for custody and/or a visitation schedule. If the mother consents to the father having legal custody the procedure will go more quickly and smoothly. He should request a consent and court approval to move the child out of state at the same time.

If you do as planned, you do not have legal custody of your child and you will encounter legal problems. You may not be able to register the child in school or obtain medical treatment without proof of legal custody. There is always the possibility that the child's mother will change her mind and accuse you of kidnapping.

You should visit the family court and ask to speak with an advocate who can advise you what you need to file. It would be better if you could consult with a private attorney who specializes in family law and custody issues in your area.