Country State Select gives you cascading Country → State/Province → City dropdowns for Rails forms: pick a country, the state field repopulates; pick a state, the city field repopulates.

Country/state/state data comes from the city-state gem (pluggable — see Custom data sources).

v4.0 is a modernization release. Highlights:

• Dependency-free JavaScript (no jQuery) with a bundled Stimulus controller
• Works with importmap-rails, Sprockets, Propshaft, or npm/esbuild/webpack
• Native form_with/form_for support (f.country_select, f.state_select, f.city_select) — simple_form is no longer required
• priority_countries, only/except filtering, flags, dial codes, I18n-localized names
• A pluggable data source adapter
• HTTP-cached JSON lookup endpoints
• An install generator (rails g country_state_select:install)

Upgrading from 3.x? See docs/migration-v4.md — the legacy jQuery/Chosen JavaScript still works, but Rails < 7.0 is no longer supported (stay on the 3.x gem for older Rails).

gem 'country_state_select'

bundle install
rails g country_state_select:install   # optional: initializer + setup instructions

Requires Rails >= 7.0 and Ruby >= 3.1.

Pick the one that matches your app. All of them talk to the same /find_states and /find_cities JSON endpoints (see docs/json-api.md).

The engine registers its pins automatically — no pin lines to write yourself. In app/javascript/application.js:

import "country_state_select"
import { Application } from "@hotwired/stimulus"
import CountryStateSelectController from "country_state_select/controller"

const application = Application.start()
application.register("country-state-select", CountryStateSelectController)

Or, with stimulus-rails' app/javascript/controllers/index.js auto-loading convention, just re-export it as its own controller file:

// app/javascript/controllers/country_state_select_controller.js
export { default } from "country_state_select/controller"

Then in a view, wrap your fields in a controller container:

<div data-controller="country-state-select">
  <%= f.country_select :country %>
  <%= f.state_select :state, :country %>
  <%= f.city_select :city, :state, :country %>
</div>

Stimulus controller values (all optional, set as data-country-state-select-<value>-value="..."):

//= require country_state_select_vanilla

document.addEventListener('DOMContentLoaded', function () {
  CountryStateSelect({ country_id: "country_field_id", state_id: "state_field_id" })
})

npm install country_state_select @hotwired/stimulus

import CountryStateSelectController from "country_state_select/controller"
// or, for the framework-agnostic core directly:
import CountryStateSelect from "country_state_select"

@hotwired/stimulus is an optional peer dependency — only needed if you import the /controller entry point.

Still bundled for apps upgrading from 3.x. New apps should use one of the options above.

//= require country_state_select
//= require chosen-jquery   // optional, if you want the Chosen UI

$(document).on('turbo:load', function () {
  CountryStateSelect({
    country_id: "country_field_id",
    state_id: "state_field_id",
    chosen_ui: true,
    chosen_options: { disable_search_threshold: 10 }
  })
})

<%= form_with model: @business do |f| %>
  <div data-controller="country-state-select">
    <%= f.country_select :country, include_blank: true %>
    <%= f.state_select :state, :country %>
    <%= f.city_select :city, :state, :country %>
  </div>
<% end %>

• state_select/city_select read the model's current country/state to render the right options server-side — on an edit form, the saved state and city show up correctly without waiting on JavaScript.
• When the parent selection has no states/cities (e.g. a country with no states), the field renders as a plain text input, same as before.
• only:, except:, and priority: options work on all three: f.country_select :country, priority: %w[US CA].

<%= simple_form_for @form_object do |f| %>
  <%= f.input :country_field, collection: CountryStateSelect.countries_collection %>

  <% options = { form: f, field_names: { country: :country_field, state: :state_field } } %>
  <%= f.input :state_field, CountryStateSelect.state_options(options) %>
<% end %>

City support: see docs/cities.md.

# config/initializers/country_state_select.rb
CountryStateSelect.configure do |config|
  config.priority_countries = %w[US CA GB]   # shown first in the dropdown
  config.only_countries = %w[US CA GB IN]    # restrict the list
  config.except_countries = %w[KP]           # or exclude specific ones

  config.flags = true          # "🇮🇳 India"
  config.dial_codes = true     # "India (+91)"
  config.localize_names = true # translate names via I18n / the `countries` gem

  config.cache_duration = 1.day # HTTP cache on /find_states, /find_cities; nil disables it
  config.draw_routes = true     # set false to mount the engine at a custom path instead
end

Every option here can also be passed per-call: CountryStateSelect.countries_collection(priority: %w[US]), f.country_select :country, only: %w[US CA].

Swap out city-state (e.g. for a database table, or the countries gem) by implementing the adapter interface:

class MyDataSource < CountryStateSelect::DataSources::Base
  def countries
    { US: 'United States', IN: 'India' } # code => English name
  end

  def states(country_code)
    [[:CA, 'California'], [:NY, 'New York']] # [code, name] pairs
  end

  def cities(state_code, country_code)
    ['Los Angeles', 'San Francisco'] # plain names
  end
end

CountryStateSelect.configure { |c| c.data_source = MyDataSource.new }

By default the engine draws /find_states and /find_cities at the top level. To mount it elsewhere:

# config/initializers/country_state_select.rb
CountryStateSelect.configure { |c| c.draw_routes = false }

# config/routes.rb
scope path: '/csc' do
  match 'find_states' => 'country_state_select/cscs#find_states', via: :get
  match 'find_cities' => 'country_state_select/cscs#find_cities', via: :get
end

Then pass the matching URLs to the JS: states_url: '/csc/find_states' (or the Stimulus states-url-value).

The lookup endpoints are documented in docs/json-api.md — useful if you're driving the selects from a SPA or mobile client instead of the bundled JS.

bundle install
bundle exec rspec

The dummy Rails app used for integration tests lives in spec/dummy and doubles as a runnable demo:

cd spec/dummy
bin/rails server

CI runs the suite across Ruby 3.1–3.4 (latest Rails) and Rails 7.0/7.1/7.2/8.0 (see gemfiles/).

Fork, fix, then send a pull request.