Example of restricting shipping to a single state for a single shipping class with WooCommerce, prepared for Evan Thorpe based on my blog post http://stevegrunwell.com/blog/woocommerce-restrict-shipping

gistfile1.php

public function is_available( $package ) {

  // Determine if we have any items in the "In-state" shipping class
  $restricted_shipping_class_slug = 'in-state';
  $permitted_states_for_restricted_items = array( 'NY' );
  $has_restricted_items = false;

  foreach ( $package as $pkg ) {
    if ( isset( $pkg['contents'] ) ) {
      foreach ( $pkg['contents'] as $contents ) {
        if ( isset( $contents['data'] ) && $contents['data']->get_shipping_class() == $restricted_shipping_class_slug ) {
          $has_restricted_items = true;
          break;
        }
      }
    }
  }

  // Limit items in the "In-state" shipping class to $permitted_states_for_restricted_items
  if ( $has_restricted_items && ! in_array( $package['destination']['state'], $permitted_states_for_restricted_items ) ) {
    return false;

  // The states/territories not permitted for this method
  $restricted = array( 'AK', 'AS', 'GU', 'HI', 'MP', 'PR', 'UM', 'VI' );
  } elseif ( in_array( $package['destination']['state'], $restricted ) ) {
    return false;
  }
  return parent::is_available( $package );
}