All actions and proceedings, civil and criminal, commenced after the organization of a new county or a county with changed boundaries, shall be begun and proceeded with therein if it would have been the proper county in which to institute the action or proceeding had it been organized before the cause for the proceedings arose.
A.R.S. § 12-402
Venue of actions commenced after organization of new county
Official source: Arizona State Legislature. Reproduced from public-domain Arizona statutes; confirm against the official source for the current text. Not legal advice.