Trewin is a surname. Notable people with the surname include:
People Dennis Trewin AO (born 1946), Australian former public servant, head of the Australian Bureau of Statistics Ion Trewin (1943–2015), British editor, publisher and author J. C. Trewin OBE (1908–1990), British journalist, writer and drama critic Kai Trewin (born 2001), Australian professional footballer Max Trewin (1927–2005), Australian rules footballer Morris Trewin, Canadian retired ice hockey goaltender Shari Trewin, computer scientist Todd Trewin (born 1958), American equestrian Tom Trewin (1914–1992), Australian politician Wendy Trewin (Wendy Monk) (1915–2000), English writer and critic
Other Trewin Brothers, a Watford, UK department store bought by national retail giant John Lewis & Partners in 1970 and closed in 2020