Sarnia is the Latin name for Guernsey. It is used in the title of the island’s anthem, Sarnia Cherie (Dear Guernsey), and the Sarnian newspaper uses it as the basis of its name.
Sarnia is also the name of a town in Ontario, Canada. Wikipedia explains how it got its name as follows:
In 1829 Sir John Colborne, a former governor of Guernsey, was appointed Lieutenant Governor of Upper Canada. In this capacity, he visited two small settlements in 1835 that had been laid out on the shores of Lake Huron. One of these, named “The Rapids,” consisted then of 44 taxpayers, nine frame houses, four log houses, two brick dwellings, two taverns and three stores. The villagers wished to change its name but were unable to agree on an alternative. The English settlers favoured the name “Buenos Aires” and the Scottish “New Glasgow”. Sir John Colborne suggested Port Sarnia. On 4 January 1836, the name was formally adopted by a vote of 26 to 16