4th (Central Ontario) Battalion, CEF was organized at Valcartier under Camp Order 241 of 2 September 1914 and was composed of recruits from Military District 2 (Aurora, Brampton, Brantford, Hamilton and Niagara Falls. The battalion was commanded by Lieutenant-Colonel W.S. Buell who was replaced within days by Lieutenant-Colonel R.H. Labatt.
The battalion embarked at Quebec on 23 September 1914 aboard TYROLIA, disembarking in England on 14 October 1914. Its strength was 44 officers and 1121 other ranks. The battalion disembarked in France on 11 February 1915, becoming part of the 1st Division, 1st Canadian Infantry Brigade. It was later reinforced by the 3rd Canadian Reserve Battalion. The battalion returned to England on 23 March 1919, disembarked in Canada on 21 April 1919, was demobilized at Toronto on 23 April 1919, and was disbanded by General Order 149 of 15 September 1920.