In 1924 the federal electoral district of Grenville was abolished when the county's riding was amalgamated with that of Dundas to become a new district known as Grenville-Dundas. In 1925 a federal election was held to determine who would be the first representative for the new electoral district in the House of Commons.
Casselman won the election with 8,175 votes to Anderson's 5,221 votes. This was the start of Casselman's 33 consecutive years as MP for Grenville-Dundas.