Viscount Weir, of Eastwood in the County of Renfrew, is a title in the Peerage of the United Kingdom. It was created in 1938 for the Scottish businessman, public servant, politician and former President of the Air Council, William Weir, 1st Baron Weir. He had already been created Baron Weir, of Eastwood in the County of Renfrew, in 1918, also in the Peerage of the United Kingdom. As of 2010 the titles are held by his grandson, the third Viscount, who succeeded his father in 1975. The family previously owned Montgreenan Mains Estate, near Torranyard, Ayrshire.