William Jefferies
- Full Name: William M. Jefferies
- Species: Human
- Gender: Male
- By 2238: Admiral, theoretical engineer, Starfleet; San Francisco Fleet Yards (TOS Novel: Errand of Vengeance: Killing Blow)
- By 2238: Project supervisor, Constitution-class development project (TOS Novel: Errand of Vengeance: Killing Blow)
- 2242: Admiral, commanding officer, Starfleet; USS Constitution (TOS Novel: Errand of Vengeance: Killing Blow)