Caroline Stewart Bond Day was born on November 18, 1889, in Montgomery, Alabama, to Georgia and Moses Stewart. The Stewart family lived in Boston for several years. After her father's death, her mother moved the family to Tuskegee, Alabama; there Georgia Stewart taught school and married John Percy Bond, a life insurance company executive. Caroline adopted her stepfather's last name. Georgia and John Bond had two children together, a daughter, Wenonah Bond Logan, and a son, Jack Bond.
Caroline Bond was introduced to the field of anthropology in a class at Radcliffe taught by Earnest A. Hooton. During her senior year, she began collecting the physiological and sociological information on 'mixed' families which would lead to her publication A Study of Some Negro-White Families in the United States (1932). In her Radcliffe yearbook and alumna record, she listed social service work, not anthropology, as her ultimate career goal. Following graduation from Radcliffe, she was employed by a variety of institutions. In 1919, she worked briefly in New York City in relief and support services for black soldiers and their families, and also served as student secretary of the National Board of the YWCA. Later that year, she moved to Waco, Texas, where she taught English at Paul Quinn College and Prairie View College in Houston, Texas.
In March of 1920, Caroline Bond married Aaron Day, a chemistry teacher at Prairie View College. He had graduated from Prairie View in 1919, and served overseas during World War I. After his marriage, Aaron Day joined the National Benefit Life Insurance Company as a salesman. Caroline Bond Day's stepfather was also employed in this company. Because of Aaron Day's frequent promotions in the life insurance business, the couple moved several times during the next two decades. In 1922, they lived in Atlanta, Georgia, where she began teaching English and drama at her alma mater, Atlanta University. She remained there until 1929. During this period, she also published some essays and short stories, including an autobiographical tale "The Pink Hat."
The research that Day began with Hooton in her senior year at Radcliffe (1919) was "continued only in her spare time" over the next thirteen years. In 1927, when Hooton received a grant from the Bureau of International Research (BIR) of Harvard University and Radcliffe College, Day received funds to support her research. While working in Hooton's lab, she collected and analyzed physiological and sociological information on 346 families, with the help of her half-sister, Wenonah Bond. This information was compiled in the 1928 manuscript "Preliminary Notes on Sociological Data for Negro-White Crosses." Day took a leave from the project because of exhaustion and a rheumatic heart condition, and returned to Atlanta University for the 1928-29 school year. She again taught English and was said to have given the first class in anthropology ever offered at Atlanta University. With a graduate fellowship from the BIR, Day returned to Radcliffe in late 1929 to complete her study, which culminated in the award of the Master of Arts degree in 1930
Day's thesis was prepared for publication in the 1932 Harvard African Studies series Varia Africana. In 1930, the Days moved to Washington, D.C., where she taught and did social work. About this time, she befriended a young boy, Bernard (b. 1926) whom the Days adopted (although not legally). Bernard took their name as his own, becoming Bernard Aaron Day. From 1930 to 1933, Caroline Bond Day taught English at Howard University. In 1934, she became director of a settlement house in Washington, D.C., and Aaron Day joined the North Carolina Mutual Life Insurance Co. In 1937, she was appointed general secretary of the Phyllis Wheatley Branch of the Washington, D.C., YWCA.
In late 1939, the Day family moved to Durham, North Carolina, where Aaron Day was promoted to the head office of the North Carolina Mutual Life Insurance Company. Caroline Bond Day taught English and drama at North Carolina College for Negroes (now North Carolina Central University), but was forced to resign due to recurrent illness. Apart from some unpublished writings and occasional brief teaching assignments, the rest of Day's life was devoted to, among other things, "gardening, specializing in the Hawaiian hybiscus [sic]." She read voraciously and participated in Durham's active club life. Although a stroke (with ensuing paralysis of an arm) hampered her bridge-playing, a friend fashioned a stand for her out of plywood to help in dealing cards. On May 5, 1948, Day died of cardiac complications. Her husband retired from North Carolina Mutual in 1960, two years after being elected Vice President and Agency Director. Aaron Day died in 1963.