Cossar is a surname. Notable people with the surname include:
George Payne Cossar (1907–1992), American lawyer and politician James Cossar Ewart (1851–1933), Scottish zoologist John Cossar (1858–1935), English actor Rose Cossar (born 1991), Canadian gymnast
This surname is being researched by a member of The Guild of One-Name Studies. https://one-name.org/
See also Cossart Cossard