G. Arthur Cooper and Josephine Wells met during the graduate degree in Geology at Yale University. They were married in 1930 and moved to Washington, DC, where Arthur was employed at the Smithsonian Institution. The Coopers lived in Washington until 1987. After rearing her family, Mrs. Cooper, (or Jo as her associates called her) made use of her geological training, working for the US Geological Survey's Names Committee in the 1950s. Jo also assisted her husband in his work at the Smithsonian for many years. In the 1960s she learned Russian and used that knowledge to translate geological articles that trickled out from behind the Iron Curtain. She became so proficient that she soon was making translations for geologists throughout the English-speaking world. As Arthur became one the pre-eminent paleontologists in the world, Jo supported his work by assisting him in his research and entertaining visiting scientists at their home. They were a team in the best sense of the word. In later life they travelled widely throughout the world.

They were survived by two children, Arthur W. and wife Jean of Raleigh and Anne Arredondo and husband Alfonso of Berkeley, CA; grandsons Paul A. Cooper of Raleigh, Roy A. Cooper and wife Susan Hill of Cary, Roger P. Gay of Los Angeles, CA, and Daniel A. Gay and wife Brenda of Greenwood, IN; granddaughter Georganna Gay of Pawlet Village, VT; five great-grandchildren, Kathryn M. Cooper of Los Angeles, CA, Chelsea A. and Benton C. Alexopoulos of Pawlet Village, VT, and Lauren T. and Henry W. Gay of Greenwood, IN.