As far as Lemmy is concerned, I just joined an instance that's relevant to my location (feddit.uk). I suppose if it grew a great deal more popular than that, I could create a community there for my local county.

I should absolutely mention though that I'm still hard at work on Habitat, which is a platform for local communities, and each post has a lat/long location associated for a more hyperlocal type of interaction. It's not on the Fediverse though (though there are plans for non-Fediverse federation).