Cavan , county (1991 pop. 52,796), 730 sq mi (1,891 sq km), N Republic of Ireland. The county seat is Cavan. The county is a hilly region of lakes (Lough Oughter chief among them) and bogs, and the climate is extremely damp and cool. Most of the soil is clay. The Erne is the principal river, and the Shannon has its source there. Pastoral agriculture is the chief occupation, although very little land is under cultivation (in the form of small farms). Industries include plastics, wallpaper, creameries, and food processing. Cavan was organized as a shire of Ulster in 1584.