William Griesinger (June 20, 1895 – April, 1978) was an Ontario merchant and political figure. He represented Windsor—Sandwich in the Legislative Assembly of Ontario from 1945 to 1959 as a Progressive Conservative member.
He was born in Windsor, Ontario, the son of Lewis Griesinger. In 1934, he married Mary Adele Allen, with whom he raised daughter Rosemary and adopted son William. He was owner and general manager of the Windsor Lumber Company. Griesinger served with the Canadian Expeditionary Force during World War I, reaching the rank of major, and was awarded the Military Cross. After the war, he continued to serve with the local militia as lieutenant-colonel. Griesinger served in the provincial cabinet as Minister Without Portfolio and Chief Commissioner of the Liquor Control Board of Ontario from 1948 to 1949, Minister of Planning and Development from 1949 to 1953 and Minister of Public Works in the provincial cabinet from 1953 to 1958.
He resigned from the provincial cabinet in 1958 after he was implicated in a stock trading scandal involving Northern Ontario Natural Gas (NONG), a natural gas company. Specifically, Premier Leslie Frost had ordered all members of his Cabinet to divest themselves of any stock in NONG, but Griesinger did not do so. Later, Premier Frost described Griesinger's involvement in the matter as a "minor indiscretion".