Petit Lac Saint-François or Lake Tomcod is a lake in the municipality of Saint-François-Xavier-de-Brompton, in regional county municipality (MRC) of Le Val-Saint-François, in the administrative region of Estrie, Quebec, Canada.

[1][2] Cyanobacteria (blue-green algae) are present in the lake.

[3] This lake borders the east side of the village of Saint-François-Xavier-de-Brompton.

It is located south of route 249 and west of highway 55.

The toponym "Petit lac Saint-François" was made official on December 5, 1968, at the Commission de toponymie du Québec.