Great project! I would, however, recommend an API with more namespaces. Functions like Address.ukCounty don't sit well with me; such an API would be a mess if you added support for countries other than the US and the UK. You could (and probably create namespaces for each country code, e.g.:

    Address
    |-> US
        |-> state
    |-> UK
        |-> state

An alternative would be for country-specific generators to take a country code as an argument. I am not an experienced API designer, though, so take my comments with a heaping of salt.