1804 to 1818.
The 100th Regiment of Foot (Prince Regent's County of Dublin Regiment) was raised in Ireland in 1804 for service in the Napoleonic Wars. After a few weeks, Lieutenant Colonel John Murray was appointed to command; he was to remain in this post for most of the regiment's active service.
The 100th were transferred to Nova Scotia in 1805, with 271 men being lost when the troopship Aeneas was wrecked off Newfoundland. They were then stationed in Canada proper. In 1807, Colonel Isaac Brock, then serving on the staff in North America, reported favourably on the regiment while they were serving as garrison for Quebec City, and commented, "The men were principally raised in the north of Ireland, and are nearly all Protestants; they are robust, active, and good looking."
During the War of 1812 the regiment served on the Canadian frontier. A detachment was present at the Battle of Sackett's Harbour in May 1813. Major George Taylor captured two 10-gun American vessels, the Growler and Eagle, on 3 June 1813 on the Sorrell River near Ile aux Noix on the Canadian side of the lake, after a fight of three-and-a-half hours; British casualties were three men wounded and American casualties were one man killed and eight severely wounded. (Both vessels were taken into Royal Navy service, but the Americans recaptured them the next year.)
The whole regiment took part in the Capture of Fort Niagara in December. From there, they were engaged on raids to Buffalo and Black Rock in late December.
In July 1814, they saw action at the Battle of Chippawa (or Street's Creek), where the regiment took heavy losses, reduced to "one Captain & 3 subalterns doing duty, with 250 effective men". They then served at the Siege of Fort Erie in the closing months of the year. For their services in the defence of Canada, they were awarded the battle honour Niagara. The Colonel of the Regiment was Brig. Sir Frederick John Falkiner, Bt.
In 1816 the regiment was renumbered the 99th Foot, then withdrawn to England in 1818 to be disbanded at Chatham. As the Napoleonic Wars ended, England was faced with thousands of returning soldiers. Rather than having them all return to England and Ireland, many of soldiers of the 100th Foot were offered and accepted land-grants in Upper Canada. The largest settlement from the 100th Foot was in Richmond, Ontario the predecessor to Ottawa, Ontario.
A later 100th Foot, the 100th (Prince of Wales's Royal Canadians) Regiment of Foot was raised in Canada in 1858 and declared the successor to this regiment in 1875; it was amalgamated in 1881 into The Prince of Wales's Leinster Regiment (Royal Canadians), which itself was disbanded in 1922.