A prefecture — an administrative division in Japan (one of the prefectures). Used as a suffix for prefecture names (e.g., Yamagata-ken).
私の実家は広島県にあります。
My parents' home is in Hiroshima Prefecture.
県庁はその県の行政の中心だ。
The prefectural office is the administrative center of that prefecture.
北海道は独自の行政区画で、他の地域のような「県」はない。
Hokkaido has a unique administrative division and does not have "ken" like other regions.