• 〜郡ぐん — 〜 county / district
• 郡県ぐんけん — counties and prefectures
• 郡役所ぐんやくしょ — county office (historical)

郡 is a phono-semantic compound: 君 (phonetic, meaning “lord” or “ruler”) provides the sound, while 阝 (place radical) provides the meaning. Historically it referred to local administrative divisions governed by appointed leaders.

郡ぐんは 県けんの下したにある 行政区画ぎょうせいくかくです。
A "郡" is an administrative district below the prefectural level.

郡部ぐんぶに 住すむ人ひとは 農業のうぎょうに 従事じゅうじしています。
People living in rural districts often work in agriculture.