noun which may take the genitive case particle 'no', noun
in the prefecture; prefectural
Used attributively (often with の) to mean 'within a prefecture' or 'prefectural'. Common in news reports and administrative language.
Disaster drills were held simultaneously at elementary and junior high schools across the prefecture.
A heavy rain warning was issued for the entire prefecture.
This high school is the largest in the prefecture.
Sports days were held at elementary schools throughout the prefecture.
県外 means 'outside the prefecture', the direct opposite of 県下's meaning of 'within the prefecture'.
Compound of 県 (prefecture) and 下 (under, within). The 下 here indicates a scope or jurisdiction, similar to its use in 管下 (under jurisdiction).