Isidore Frégeau (December 9, 1833 – September 2, 1906) was a physician and political figure in Quebec.
He represented Shefford in the Legislative Assembly of Quebec from 1881 to 1886 as a Conservative.
He was born in Saint-Pie, the son of Jean-Baptiste Frégeau and Angélique Lemonde.
He qualified to practise medicine in 1861 and practised in North Stukely, Lawrenceville, Waterloo and Sherbrooke.
He was married twice: to Marie-Onésime-Caroline Tétro-Ducharme in 1862 and to Hermine Simoneau in 1887.