Somby is a commom sami lastname. The name are most likely been made as an norwegianized variation based on the sami town Sombio (or Sompio) in the Kemi region of north Finland. The name has probably also rised from the personal male name like Sompia, Sompi, Sombie, Sombe Sombby, Sombi, Sumby and Sobbe. The name has been used as a family name written as Sombio, Sompio, Sombi and Somby.
Somby is the most common form today. It occurs basically in the nort-norwegian communities of Kautokeino and Karasjok, but also in the northern-scandinavian region. The ancestor of the Somby family is Oloff Persson Sombio, registrated in Kautokeino from 1697 to 1707.
Source
Kautokeinoslekter, by Adolf Steen. Renewed by Ola Aarseth (1986)