Shepherd's pie derives its name from its primary meat content, which is traditionally either lamb or mutton. Similar dishes with beef or other meat as a featured ingredient are more correctly called cottage pie. Both dishes likely date back to the 1700s, although the earliest recorded use of the name dates to the 1870s, states CooksInfo.com.
While it is often assumed that the name derives from the fact that shepherds tend the sheep that feature in the pie's filling, this may be purely descriptive or it may be adaptive folk etymology. It also is widely speculated that meat pies of various kinds were called cottage pies until the 1870s, when the name "shepherd's pie" emerged and the term became common.
Neither cottage pie nor shepherd's pie could have originated before potatoes became generally accepted in the United Kingdom, which wasn't until the end of the 1700s, CooksInfo.com speculates. Before that, a similar dish was made in Scotland, but this was topped with a pastry crust instead of mashed potato.
The simple, hearty peasant dish now commonly defined as shepherd's pie likely originated in Scotland and the North of England. It may well have come from the Lake District, where some of the best free-range Herdwick lamb and mutton is raised and the locals are very proud of their shepherding heritage, according to Fellwalker.