It is located approximately 100 kilometres (62 miles) south of Ottawa and is midway between Kingston and Montreal, Quebec.

The county was named in 1792 to honour Henry Dundas, who was Lord Advocate for Scotland and Colonial Secretary at the time.

As well, the Dundas Militia built numerous earthworks and breastworks along the river to fortify the area from attack, in 1814, the earthwork at Point Iroquois was expanded to include a blockhouse, but due to the construction so late in the war, and the relative peace, the fort was called Fort Needless.

[2] James Pliny Whitney, Ontario's sixth premier, is buried here in the cemetery of Holy Trinity Anglican Church in Riverside Heights, just east of Morrisburg and north of County Road 2 (formerly Highway 2).

Whitney was born in Williamsburg in 1843, represented Dundas County in the Legislature from 1888 to 1914 and served as Premier from 1905 to 1914.

Unlike the Lost Villages of Cornwall and Osnabruck Townships, however, the two towns were simply relocated to higher ground in the same area.

In 1976, stuntman Ken Carter attempted to jump a one-mile portion of the Saint Lawrence River by taking a one million dollar Lincoln Continental rocket car off an eight-storey ramp.

The municipality was established on January 1, 1998, with the amalgamation of the former townships of Matilda and Williamsburg, along with the former villages of Iroquois and Morrisburg.