These forms and instructions are available in the General Clerk's Office, Room 108, in the Nassau County. You should file the custody petition in the Bronx.Contact the clerk's office or Family Legal Care's Helpline at 1-800-696-8629 to learn more. This file provides essential instructions for creating a petition for custody or visitation. A petition for custody would be filed in the juvenile, family, or domestic relations Court with jurisdiction over the child, at the county level. These are documents and forms relating to the areas in which they are located. Most documents and forms on this website are in Adobe Acrobat (.