Father Alexander Macdonell, later bishop of Upper Canada, began Alexandria (first known as Priest's Mills) as a mill site a few years after the War of 1812. In 1890, it became the seat of the Roman Catholic diocese of Alexandria (later relocated to Cornwall). Around that time it showed much promise in carriage manufacturing.
After economic setbacks in the Great Depression and earlier, since the Second World War has regained a considerable degree of prosperity with a concentration on textiles, footwear, milk processing and trucking. It continues its early role as a merchandising and service centre for the surrounding farm community. About half of Alexandria’s residents have French as their mother tongue, according to the 2016 census, but both English and French are spoken. St. Finnan's Cathedral, the Bishop's Palace and the Monastery of the Precious Blood are of architectural interest.