On June 17, 2021, the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) was notified of a confirmed case of eastern equine encephalitis (EEE) in a 26-year-old horse located in the United Counties of Stormont, Dundas and Glengarry. The unvaccinated horse developed intermittent bouts of recumbency with somnolence and mild muscle fasciculations with periods of normal behaviour and mentation in between. These signs occurred over the course of several days. The horse is recovering. Laboratory diagnostic testing confirmed infection with the EEE virus (EEEv).