Sara Cosette Billey (born February 6, 1968 in Alva, Oklahoma, United States) is an American mathematician working in algebraic combinatorics. She is known for her contributions on Schubert polynomials, singular loci of Schubert varieties, Kostant polynomials, and Kazhdan–Lusztig polynomials often using computer verified proofs. She is currently a professor of mathematics at the University of Washington. In 2012, she became a fellow of the American Mathematical Society.