Elizabeth Posthuma Gwillim (1762 (or 1766?)-1850) was the wife of John Graves Simcoe. She named the Scarborough, Ontario area of the Greater Toronto Area after Scarborough, England. They had four daughters.

She was born to Elizabeth Spinckes and Lieutenant Colonel Thomas Gwillim. Elizabeth's father died months before her birth and her mother died shortly after her birth. Elizabeth was given the name Posthuma in commemoration of her mother. She was baptized the same day as her mother's burial. Her mother’s younger sister Margaret, who married Admiral Samuel Graves in 1769, took Elizaeth into her care.

She met John Simcoe in 1782 and married him that year.