Leeds—Grenville—Thousand Islands and Rideau Lakes is a provincial electoral district in Ontario, Canada, that has been represented in the Legislative Assembly of Ontario since 1987. Before the 2018 election, it was known simply as Leeds—Grenville. It consists of the United Counties of Leeds and Grenville. Since 1999, provincial ridings have been defined to have the same borders as federal ridings. For the 2018 election, the district gave up a small portion of territory to Lanark—Frontenac—Kingston.