Rails’ country_select form helper doesn’t accept a :selected option. If a validation error occurs, you really don’t want to force the user to reselect a country. However, there’s no documented way of persisting that data when re-rendering an unvalidated form.

Fortunately, the country_select helper accepts a parameter called priority_countries. This exists so you don’t have to scroll all the way down past Uganda and Ukraine just to arrive at the good ol’ US of A. A clever workaround to this problem is to use the priority_countries parameter to effectively “select” the previous value through a bit of magic.

<%= form.country_select :country,
  [@location['country'] || 'United States'] %>

This ERb line merely appends your selected country to the top of the priority country list. And, indeed this allows your old country to remain selected even if a validation errors causes the form to be rendered again.