 Arza Clair Casselman was born January 19, 1891 in Mariatown, Ontario, located in what was then Williamsburg Township (now, the municipality of South Dundas) in the United Counties of Stormont, Dundas and Glengarry.Casselman was the son of Michael and Almeda Casselman, who were married in 1872.His mother Almeda was born in Williamsburg Township in 1851 and his father Michael was born in Matilda Township in 1848, now also part of South Dundas.