noun
entire prefecture; the whole prefecture
Refers to the whole area of a single prefecture. Often used in news or administrative contexts.
全県に大雨警報が出された。
A heavy rain warning was issued for the entire prefecture.
noun
every prefecture; all prefectures
Refers to all prefectures in a given context, such as nationwide surveys or comparisons.
全県で学力テストが実施された。
Academic achievement tests were conducted in every prefecture.
Compound of 全 (zen, 'all, entire') and 県 (ken, 'prefecture'). The meaning depends on whether 全 modifies a single prefecture or a group of prefectures.