(a) Dependency proceedings shall be commenced in the county where the child resides, in the county where the child is present when the proceedings are commenced, or in the county where the acts that are the basis of the dependency petition occurred.
(b) Regardless of the county where the child currently resides, when a petition is filed seeking to modify an award of custody or visitation pursuant to an adjudication of dependency, and one of the individuals who was a party to the original proceeding still resides in the county of the juvenile court of original jurisdiction, the petition shall be filed in the juvenile court of the original jurisdiction.
(c) When a petition is filed seeking to modify an award of custody or visitation pursuant to an adjudication of dependency in which all parties to the original action, including the child, no longer reside in the county of original jurisdiction, the petition shall be filed in the county where the child resides at the time the petition is filed. The petition shall be accompanied by a certified copy of the most recent order to be modified.
(d) For purposes of this section, county where the child resides means the county in which the child and legal custodian have established legal residence or have resided for six or more months of a calendar year. This term shall not include placements by a state department or agency.