Wikipedia page - (I bet Mary would have spent a lot of time on Wikipedia if it had been invented by 1916)

Biography at MacTutor - Biography with links, bibliography, and writing extracts - including the full text of Mary's correspondence with Darwin!

Profile hosted by St. Agnes College - Short bio with references; includes a linked image of the extremely weird Garfield cartoon that pays tribute (?) to Mary

Essay by Sydney Birbrower on Medium - Fun, funny bio that seems to be super well-researched and has some great tidbits I hadn't read elsewhere online!

String Art Magic by Rain Blanken - The author of this string art how-to traced the history of her craft back to Mary's curve stitching, and apparently interviewed a great-granddaughter of the Booles to include a section on Mary. Wow, neat! I just ordered my copy! (from a local bookstore tho tbh I hate amazon)

Darwin Correspondence Project page - Short blurb on Mary, with links to Cambridge University Library's fancy officially citable transcriptions of the letters between her and Darwin

Collected Works Review - In 1931, Mary's collected works were published in a four-volume edition. Dorothy Maud Wrinch's review of the collection for the Mathematical Gazette is a great descriptive summary of Mary's work, and a snapshot of how it was received in the decades following her death.