What is the origin of the surname Lewis?

The specific origins of Lewis are unclear, as there are several interrelated histories. It clearly evolved in the British Isles, with strong evidence that it emanates from Wales & Scotland. The Lewis family seems to have roots in Ireland & England as well.

The Isle of Lewisi is one of multiple islands that are collectively known as the Hebrides, or the Western Isles, located off the western coast of Scotland.

Originally known as Leodhas in Gaelic (still very commonly spoken in the Hebrides, Leodhas means "Marsh"). The islands offer chilling weather, are very wet, and as such, it is possible to draw the linguistic evolution between the Gaelic word for "Marsh" (Leodhas) with Leod of MacLeod, as well as Lewis.

Up until about 1500 BC, the island had predictable weather that made for good farming. A volcanic eruption in Iceland (Mt. Hekla) produced much ash and was particularly devastating to the Hebrides. This is thought to have marked the first emigration of the Lewis peoples, probably to the south (Wales), as well as the rest of the British isles.

In 800 AD, the Hebrides began to experience Viking incursions from their Scandinavian neighbors, and this furthered the Lewis diaspora.

The Lewis families were early immigrants to the American colonies, particularly the Carolinas, Georgia, and Virginia.

The Lewis name today is also prevalent among descendants of former slaves in North America. Several noteworthy members of the Lewis family were key operators of the underground railroad that sought to smuggle slaves out of the south into the North, and there were also several large plantations owned by members of the Lewis family. As such, many slaves and former slaves took the Lewis surname, either to identify with the plantations from which they came, or to honor those who helped bring them to freedom.