William Douglas may be one of several people:

• William Douglas, 1st Earl of Douglas (c.1327-1384)
• William Douglas, 6th Earl of Douglas (1425-1440)
• William Douglas, 8th Earl of Douglas (1425-1452)
• William Douglas, Duke of Hamilton (1635-1694)
• William Lewis Douglas, governor of Massachusetts from 1905 until 1906
• William Orville Douglas, jurist and United States Supreme Court justice
• William Douglas, Castle Douglas, Scottish landowner and founder of Castle Douglas
• William Sholto Douglas, 1st Baron Douglas of Kirtleside, senior commander in the Royal Air Force
• William Douglas (c.1672-1748), probable author of the poem Annie Laurie