Saint-Louis-du-Ha! Ha! () is a parish municipality in the Témiscouata Regional County Municipality of the Bas-Saint-Laurent region of Quebec. The population is 1,311 as of 2021. Its economy is mainly agricultural. It is located southeast of Rivière-du-Loup and west of Cabano along the Trans-Canada Highway (A-85), about halfway to Edmundston in New Brunswick.
The Commission de toponymie du Québec asserts that the parish's name refers to nearby Lake Témiscouata, the sense of ha-ha here being an archaic French word for an impasse. The Louis may refer to Louis Marquis, one of the first colonists of the region, or Louis-Antoine Proulx, vicar of Rivière-du-Loup, or perhaps the abbé Louis-Nicolas Bernier.
Saint-Louis-du-Ha! Ha! is the only town in the world with two exclamation marks in its name. (Westward Ho!, in Devon, England has a single exclamation mark in its name.) In September 2017, the municipality established a Guinness World Record for the most exclamation marks in a town name.
The parish began in 1860 as the site of a Catholic mission; it was named in 1874.
In the 2021 Census of Population conducted by Statistics Canada, Saint-Louis-du-Ha! Ha! had a population of living in of its total private dwellings, a change of from its 2016 population of . With a land area of , it had a population density of in 2021.