The Stouffville Lacrosse Association is a non-profit lacrosse association which is part of the larger Ontario Lacrosse Association. Our association’s boundaries cover Stouffville, Markham, Richmond Hill, Thornhill and Unionville. Thunder  lacrosse was formed in 1962 and over the years has received a number of Provincial banners as recently as 2016 with our Intermediate team winning the B Provincials.

Lacrosse, together with hockey, shares recognition as one of Canada’s two official National sports. Its origins date back hundreds of years. The Canadian Lacrosse Association today recognizes four separate disciplines in the game of Lacrosse: Box, Men's Field, Women's Field and Inter-Lacrosse. Box Lacrosse is uniquely a Canadian game and is best described as a game of speed and reaction. Men's Field Lacrosse is a game of patience and strategy which focuses on control of the ball. The Women's Field game has stayed truest to the original sport in its play. It is a game based on the skills of passing and ball control. Inter-Lacrosse is a non-contact version of the sport designed to be adaptable to the various age and skill levels of the participants.

Lacrosse was re-confirmed by Parliament as the National (Summer) Sport of Canada in 1994.