No study has evaluated whether such associations vary by race or hormone therapy (HT) use.<h4>Objective</h4>To examine associations of baseline plasma p-tau217 with incident MCI and dementia and determine whether associations vary by age, race, APOE ε4 carrier status, or HT use.<h4>Design, setting, and participants</h4>This cohort study examined women recruited from 39 US clinical sites between 1996 and 1999 into the Women's Health Initiative Memory Study who were randomized to either estrogen alone vs placebo or estrogen plus progestin vs placebo. This evidence concerns the gene APOE and dementia.