Sarnia is a city in Ontario, Canada.

Sarnia may also refer to:

• Sarnia—Lambton (federal electoral district), Ontario, Canada, formerly known as Sarnia, a federal electoral district
• Sarnia—Lambton (provincial electoral district), Ontario, Canada, a provincial electoral district
  • Sarnia (provincial electoral district), Ontario, a riding from 1966 to 1996, which was combined with part of Lambton to create the Sarnia—Lambton provincial electoral district
• Sarnia 45 Indian Reserve of the Aamjiwnaang First Nation, Ontario
• Rural Municipality of Sarnia No. 221, Saskatchewan, Canada
• Sarnia, the Roman name for the island of Guernsey, Channel Islands

• Sarnia Sting, a junior ice hockey team
• Sarnia Legionnaires (1954–70), a junior ice hockey team
• Sarnia Legionnaires (1969–), a junior ice hockey team
  • Sarnia Arena, home arena of the Legionnaires
• Sarnia Imperials, a football team from 1928 to 1955

• HMCS Sarnia, a Second World War Royal Canadian Navy minesweeper
• SS Sarnia (1910), a passenger vessel which also served in the First World War as HMS Sarnia
• Sarnia station, Sarnia, Ontario, a Via Rail train station
• Sarnia Chris Hadfield Airport, near Sarnia, Ontario
• Sarnia: An Island Sequence, a set of three piano solo pieces by John Ireland
• Sarnia, a novel by British author John Christopher (pen name of Samuel Youd)