Beauharnois is a city in the Beauharnois-Salaberry Regional County Municipality of southwestern Quebec, Canada, and is part of the Greater Montreal Area. The city's population as of the Canada 2011 Census was 12,011. It is home to the Beauharnois Hydroelectric Power Station and the Beauharnois Lock of the Saint Lawrence Seaway.
The Battle of Beauharnois was fought at Beauharnois in 1838 between Lower Canada loyalists and Patriote rebels.
Katherine Jane "Janie" Ellice (née Balfour; 1813 – 13 April 1864) was a British diarist and artist. She is most remembered for her chronicle and watercolours of a trip to Canada in 1838, where she and her sister were taken prisoner during the Battle of Beauharnois.