Wilhelmus is a Dutch given name and surname. It may refer to:

People with the given name Wilhelmus

• Wilhelmus à Brakel (1635–1711), Dutch Protestant Reformation theologian and minister
• Wilhelmus Beekman (1623–1707), Dutch-US polititian
• Wilhelmus Bekkers (1890–1957), Dutch tug-of-war Olympic medalist and swimming instructor
• Wilhelmus Beurs (1656–1700), Dutch Golden Age painter
• Wilhelmus Bryan (born ?), US documentary film producer
• Wilhelmus Demarteau (1917–2012), Dutch Roman Catholic prelate
• Wilhelmus Doll (1900–1980), Dutch wrestler and Olympic competitor
• Wilhelmus Frederik van Leeuwen (1860–1930), Dutch politician, mayor of Amsterdam (1901-10), and lawyer
• Wilhelmus Luijpen (1922–1980), Dutch philosopher and Catholic priest
• Wilhelmus Luxemburg (born 1929), Netherlands-born US mathematician
• Wilhelmus Nuyens (1823–1894), Dutch historian
• Wilhelmus Wilhelmius (1720–1771), Dutch minister, mathematician, and philosopher
• Wilhelmus Zakaria Johannes (1895–1952), Indonesian radiologist

People with the surname Wilhelmus

• Joop Wilhelmus (1943–1994), Dutch pornographer and entrepreneur

Other

• De Wilhelmus, the grand ducal anthem of Luxembourg
• Fort Wilhelmus, a fort on Burlington Island, New Jersey, USA
• Wilhelmus (full title: Wilhelmus van Nassouwe), the national anthem of the Kingdom of the Netherlands