Courts may only decide cases that fall within their jurisdiction. "Jurisdiction" provides the boundaries for the court's reach. Venue determines the most convenient and appropriate county for a case. Disputes between states always involve jurisdiction. Disputes between counties within a state often involve venue. So, decisions between counties in Pennsylvania are generally a question of proper venue. .
Custody law is largely state law and so it can differ from state to state. Custody cases are especially susceptible to damaging jurisdictional disputes between states. So, many states have individually adopted the Uniform Child Custody Jurisdiction and Enforcement Act (the "UCCJEA"). This gives the various states the same law when deciding jurisdictional disputes. In disputes between states, the UCCJEA will determine which state has "personal jurisdiction" between the litigants. The Court must have both "subject matter" and "personal jurisdiction" but every state has subject matter jurisdiction over its own custody cases. .
Pennsylvania Courts have determined that venue squabbles between various Pennsylvania Counties will also be determined by the UCCJEA. So, disputes between counties within Pennsylvania use the same rules as disputes between the states.
In the case of J.K. v. W.L.K,, 102 A3d 511 (Pa Super 2014), the parties separated and obtained a custody order in 2011 from Chester County. The parties had both moved to Montgomery County. So, Father filed a Petition to Transfer Jurisdiction with Chester County. Although the parties had resided in Montgomery for about two years, Chester County refused to relinquish the case.
Chester County had the original jurisdiction and the original court order. So, under the UCCJEA, Chester County would generally continue to have exclusive venue to modify that custody order unless one of two things happen: (1) the Chester County court finds the the parties and child no longer have significant contacts with Chester County and substantial evidence is no longer available in Chester County; OR (2) the parties and child all reside outside of Chester County.
In this case, Chester County clearly no longer had jurisdiction because the parties and child no longer resided in Chester County. Moreover, the Chester Court did not have any finding on whether substantial evidence still remained in Chester Court. Also, the Chester Court did not have the ability to decide convenience since it did not have venue. So, the Pennsylvania Superior Court determined that Montgomery County would be the site for custody modification.
In other words, if all parties move from the original county to a new county, then the modification case may be filed in the new county. Note however that 23 PaCSA 5328 permits a court to decline otherwise good jurisdiction for "unjustifiable conduct" by a parent, such as absconding with the children.
Why did Chester not relinquish venue? It may be related to Father's legal attempts which (for example) mislabeled "venue" as "jurisdiction". Also, sometimes a county may be reluctant to relinquish venue when a party has behaved poorly in that county. In any event, it is always best to have an experienced attorney who knows the written (and unwritten} rules governing a Pennsylvania custody dispute.