Plessis, Plessy, du Plessis, and de Plessis are related French surnames, and may refer to:
- Cardinal Richelieu, French statesman and cardinal, born Armand-Jean du Plessis, Seigneur de Richelieu
- Phillipe de Plessis, French knight and 13th Grand Master of the Knights Templar
- Armand-Emmanuel du Plessis, Duc de Richelieu, French statesman
- Alphonse-Louis du Plessis de Richelieu, French bishop
- Jacques de Rougé du Plessis-Bellière, French general
- Suzanne, Marquise du Plessis-Bellière, wife of Jacques and political opponent of Louis XIV
- Marie Duplessis, French courtesan
- Gilbert de Choiseul Duplessis Praslin, French bishop
- Caesar, duc de Choiseul, Marshal of France, born Cæsar Choiseul du Plessis-Praslin
- Philippe de Mornay, French Protestant writer, also known as Mornay Du Plessis
- Joseph-Octave Plessis, Canadian bishop
- Homer Plessy, American litigant, plaintiff in the landmark Plessy v. Ferguson Supreme Court decision
- Damien Plessis, French footballer
- Guillaume Plessis, French footballer from Réunion
- Jan du Plessis, British-South African businessman
- Bismarck du Plessis and Jannie du Plessis, brothers and South African rugby players
- Koos du Plessis, South African songwriter
- Corne Du Plessis, South African sprinter
- Christian du Plessis, South African baritone
- Francois du Plessis, a South African cricketer
- Johannes du Plessis, a South African DRC missionary
- David du Plessis, a South African Pentecostal minister
- Tinus du Plessis, a Namibian rugby player
- Thomas-Antoine de Mauduit du Plessis, a French officer who fought in the American Revolutionary War
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