A valley of Perth and Kinross, Strath Earn extends over the basin of the River Earn and its tributaries, from Balquhidder in the west to the Firth of Tay in the east. It is over 30 miles (48 km) in length and averages 8 miles (13 km) in breadth. The principal settlements of Strathearn are (west to east) Lochearnhead, St. Fillans, Comrie, Crieff, Muthill, Auchterarder, Dunning, Forteviot, Forgandenny, Bridge of Earn and Abernethy. There are several fine examples of oxbow lakes and abandoned meanders in Strath Earn, especially to the north and west of Forgandenny.
Historically Strath Earn was the seat of a Celtic earldom and formed with Menteith the ancient province of Fortrenn. It later formed a stewartry in the lands of the Earls of Perth and gave its name to one of the dukedoms held by Queen Victoria's father. In 2011, the Earldom was bestowed on HRH Prince William on the occasion of his marriage.