Ch. 88, Laws of 2002, now specifically authorizes a metropolitan park district to be formed that includes areas outside of the city, or even in another city or county. Previously, the statutes relating to formation of such a district only permitted creating a district that was "coextensive with the limits of the city." (RCW 35.61.020) Any territory annexed to a city that lies entirely within the limits of a metropolitan park district shall be deemed to be within the limits of the (expanded) park district. Formation or extension of park district boundaries is no longer subject to boundary review board (BRB) review if only city territory is involved, independent of the board's review of the city annexation (RCW 35.61.250). (A proposed district that involves area within a county will still be subject to a BRB review in counties that still have a BRB).

There are two basic methods for the formation of a metropolitan park district. The city may initiate council district formation by adopting a resolution submitting a proposition for its formation to voters within the district boundaries. If the district includes area within the county or other cities and counties, the legislative body of each city and/or county which includes a portion or all of the area in the district must adopt a resolution submitting the proposition to the voters.

Alternately, a metropolitan district may be initiated via a petition with the signatures of fifteen percent of the registered voters of the city (or area of the proposed district). The petition must be submitted to the county, and the proposition is then submitted to the voters of the city at any general, special, or city election (RCW 35.61.020). Where the petition is for creation of a district in more than one county, the original petition is filed with the county having the greater area within the district and a copy filed with each other county auditor.