If it shows up as a region when searching via https://nominatim.openstreetmap.org then this process will work. This includes countries, states, counties, cities, parks, and more. OpenStreetMap can be a very valuable tool for map data (the Wikipedia of maps, in a way.)
Free-handing the polygons via the WP Google Maps polygon editor is an option (click to place/remove points, etc. when adding/editing a polygon on a map), but below gets officially detailed & accurate data that prevents overlapping, gaps, and can save time depending on how accurate you want the polygon(s) to be. Below involves a fair number of steps, but this should be the entire process & each step should be rather quick.
- Do a search for the