For elections to Renfrewshire Council, Bridge of Weir is part of ward 10, named 'Bishopton, Bridge of Weir and Langbank', which elects three of Renfrewshire's forty councillors.
Sir William is the son of Sir James Lithgow, 1st Baronet, and Lady Gwendolyn Lithgow, whose family homes were Gleddoch House, at Langbank on the Clyde, a few miles from their shipyards at Port Glasgow, and Ormsary, their country estate in Knapdale.