The school opened in 1891 as Williams Memorial Institute (WMI), which remains the legal name of the school. It was privately endowed by a bequest of real estate and personal property from the estate of Harriet Peck Williams as a memorial to her son, Thomas W. Williams II. The school was created as a high school for “the promotion and advancement of female education" at a time when few saw it as a priority.
WMI served as the high school for girls of New London and several surrounding towns. Tuition for attending students was paid by the City of New London and other towns. With the opening of New London High School in 1951, the WMI program became college preparatory rather than comprehensive. In 1954, the School moved to its present location on the Connecticut College campus. A middle school was added in 1955. In 1971, the school became coeducational. The school remains an independent day school and the present student population of approximately 230 students historically hale from over 40 local communities in CT and RI, and China.
The Williams School does not discriminate on the basis of race, color, religion, national origin, gender, gender identity, sexual orientation, age, marital status, veteran status, disability status, or any other characteristic protected by law.