Castlederg (earlier Caslanadergy, from Irish Caisleán na Deirge, meaning 'castle on the Derg')[2] is a town in County Tyrone, Northern Ireland.

It stands in the townlands of Castlesessagh and Churchtown,[3] in the historic barony of Omagh West and the civil parish of Urney.

Castlederg was a traveller's stop along the ancient pilgrimage route to Station Island on Lough Derg.

The Castlederg area, lying within the new barony of Omagh, was granted to the English Attorney-General for Ireland, Sir John Davies.

On 22 July, Armagh reported 31.4 °C (88.5 °F) which has since been rejected by the UK Met Office, meaning Castlederg holds both the highest and lowest temperature records in Northern Ireland.