emeraldmedia on "Query posts using author custom meta"

I have a custom user meta field called 'county'
I have a custom post type called 'classes'

I want to query classes by all users whose 'county' meta is the same as the page ID.

Where I'm stuck is the post query. I'm using 'author__in' which expects an array of user ID's. How do I do a user query here that will return an array of ID's?

$this_county = $post->post_name; //Use the ID of this page to determine which county we need
$user_query = new WP_User_Query( array('meta_key' => 'county', 'meta_value' => $this_county) ); //Find users whose county is set to this county
$args = array('author__in' => $user_query, 'post_type'=>'classes'); //Find classes by matched users