Jessie MacWilliams (1917 - 1990) British mathematician, best known for her work on error-correcting codes with Neil Sloane at the Bell Labs.

Born in Stoke-on-Trent, MacWilliams earned a bachelor's and a master's degree from Cambridge, then moved to the United States to continue her education at Harvard. After Harvard she began working at Bell Labs, where she assisted Sloane and co-authored with him The Theory of Error-Correcting Codes.

Because of her work with Sloane, one might guess MacWilliams has Erdos number 3, but there's actually an even shorter path: With Jacobus Hendricus van Lint, MacWilliams wrote a paper on ``Generalized quadratic residue codes'' for IEEE Trans. Inform. Theory 24. Lint in turn wrote with Erdos ``On the number of positive integers $\leq x$ and free of prime factors $> y$ ' in Simon Stevin 40.