Lilia Mary Casis, teacher, dean, and language scholar, was born in Kingston, Jamaica, on May 12, 1869, the daughter of José Marie Salomé and Coelestine Auguste Marie (Sack) de Casís. Her father, a wealthy lawyer, was of Spanish and French descent; her mother was a German related to the Kleberg family in Texas. Lilia received most of her early education, which included extensive training in classical and modern languages, from her father at home. She hoped to study medicine but when her father died, Lilia, at age nineteen, began private tutoring to supplement her family's income. In 1890 she, her mother, and her younger sister Josephine moved to Texas. Their mother died soon after their arrival, and the Casis sisters supported themselves in various teaching jobs in rural areas.
In 1894 Lilia Casis entered the University of Texas in Austin; by placing out of many classes through examinations, she completed her bachelor's degree in one year. In 1896, while holding the first student assistantship offered in the modern language department, she completed her master's degree in Romance languages, and in that same year the university named her a tutor in that subject. She was affiliated with the University of Texas for the rest of her life, as she became an instructor (1897), adjunct professor (1899), and associate professor (1908). She was appointed a full professor in 1916 and served as dean of women from 1919 to 1921. Casis additionally studied at the University of Chicago in summers and for a year in France and Spain. Her teaching specialties included elementary language courses as well as advanced linguistics and classical Spanish literature. She also wrote several articles and textbooks.
She was raised Catholic but later became a Methodist. She was a member of the Delta Kappa Gamma Society, an honorary organization for women teachers, and also was active in the YMCA, YWCA, University Ladies Club, and American Association of University Women. In 1945 she was named an honorary life member of the Texas State Historical Association. When she retired to part-time service in 1939, her friends and colleagues established a scholarship in her name. Shortly before her death Casis made the university the beneficiary of her life insurance policy and stipulated that this money was to be used for an annual scholarship for graduate study in Spanish. In addition, both Casis sisters left large sums of money to the university and the Austin school district.
Lilia Casis died in Austin on October 19, 1947, a few months after the death of her sister. She was buried in Oakwood Cemetery, Austin. In 1951 the Austin Independent School District dedicated Casis Elementary School, named for Lilia and Josephine, who was a longtime teacher in the Austin schools. The school was opened as a cooperative effort between the Austin Independent School District and the University of Texas; in addition to serving the children in its West Austin neighborhood, it included special facilities for physically handicapped students from across the city. For many years the school served as a demonstration center for the university and was noted for its trilingual classes (English, French, and Spanish) and for offering the only public kindergarten and only summer school for Austin elementary students.