Regional play doesn't quite work like that, sadly. Community services cannot extend past a city's borders. You do have options for moving electricity, water, and garbage across tiles, as well as commuters, of course.
There is a solid amount of custom content available to make it almost seem this way though. Things like civics with multiple purposes, or schools that serve elementary and high school students. Civics with wider radii can also help give this county feeling, at least for tiles with small to medium populations.
