When a user selects their country, the state drop-down will populate with all fo the states in that country. When they select a state the city drop-down will populate with all of the cities in that state.

The data is populated from the GeoData Solutions Rest API. Basic access is free and currently does not require any authentication. Just install this plugin and add the fields to your forms.

This plugin ensures users submit consistent data. For example, some may submit "PA" or "Pennsylvania" as a state or even in many cases mis-spell a state or city. We built this plugin so we could eliminate inconsistent submissions when mapping address submissions to database tables of other extensions.