County town of castlebar has the most populous city/town?
CREATE TABLE "list_of_counties" (
  "county" text,
  "irish_name" text,
  "county_town" text,
  "most_populous_city_town" text,
  "province" text,
  "region" text
);
SELECT "most_populous_city_town" FROM "list_of_counties" WHERE "county_town"='castlebar';