 His family was likely descended from the first Casselmans to settle in Dundas County, who arrived in Canada around 1784 from the Mohawk Valley, New York, as United Empire Loyalists.Casselman's father Michael was also involved in politics, but at the municipal level.Michael Casselman was elected to the Stormont, Dundas and Glengarry Counties Council in 1899 and was chosen as Counties Warden in 1903.