The courthouse and prison contributed to the importance of L’Orignal. Built in the neo-classical loyalist style, it is the oldest existing Courthouse in Ontario, and its adjacent jail was still in use until 1998. After the Ottawa District was created in 1816, hearings of the Court of Quarter Sessions of the Peace were first held in Longueuil Township. Then, in 1824 Jacob Marston donated a piece of land in the Village for the usage of the Court. The central section of the Courthouse was built by contractors McDonald and Beckworth in 1825. The building was enlarged several times, notably in 1850 and 1862. Five prisoners were hanged at the jail, the last two in 1933. When it closed in 1998, the Jail was the only francophone detention centre in Ontario.
In 2007, L’Orignal Old Jail became an interpretive centre open to visitors while the Courthouse, itself, still holds trials with or without a jury.