Alliston is a settlement in Simcoe County in the Canadian province of Ontario. It is part of the Town of New Tecumseth, the 1991 amalgamation of Alliston and nearby villages Beeton, Tottenham, and the Township of Tecumseth. The primary downtown area is located along Highway 89, or Victoria Street.

The town grew as a commercial centre for the area farmers and was best known as a potato-growing area. It is still a major industry in the town and is celebrated by the annual Alliston Potato Festival. Honda of Canada Manufacturing operates a large auto manufacturing facility southeast of Alliston, currently consisting of three major factories. Due to the falling economy Honda had to lay off all of its temporary and contract workers, striking a huge uproar among the residents of New Tecumseth.

Earl Rowe Provincial Park is located three kilometers west of Alliston, in the amalgamated Township of Adjala-Tosorontio. It is one of the largest provincial parks in Southern Ontario.