Middlesex was a provincial riding in Ontario, Canada, that was created for the 1975 election.

In 1975, the boundaries of the riding included the townships of Caradoc, Delaware, Ekrid, Lobo, London, Metcalfe, Mosa, North Dorchester, Westminster and West Nissouri.

It also included the town of Strathroy and the villages of Glencoe, Newbury and Wardsville.

[1] In 1986, the boundaries were changed as follows: it was realigned to include Indian reserves No.

[2] In 1996, the provincial government reduced the number of ridings in the province from 130 to 103.