Johnsen is a Danish-Norwegian patronymic surname meaning "son of John". Notable people with the surname include:

• Arne Odd Johnsen (1909–1985), Norwegian medieval and economic historian
• Arve Johnsen (born 1934), Norwegian industrial executive and politician
• Bent Inge Johnsen, Norwegian footballer
• Bjarne Johnsen (1892–1984), Norwegian gymnast, 1912 Summer Olympics
• Britton Johnsen (born 1979), American professional basketball player
• Christian Johnsen (born 1977), Norwegian footballer and football manager
• Dawn Johnsen, American lawyer
• Egil Børre Johnsen, Norwegian writer
• Erik Johnsen (born 1965), Norwegian ski jumper
• Erland Johnsen (born 1967), Norwegian footballer and football coach
• Espen Johnsen (born 1979), Norwegian footballer
• Espen Johnsen (politician) (born 1976), Norwegian Member of Parliament for Oppland
• Frode Johnsen (born 1974), Norwegian player of the Japanese football club Nagoya Grampus Eight
• Gina Johnsen, American politician from Michigan
• Görel Johnsen (born 1949), manager of the band ABBA
• Grethe Gynnild Johnsen, Norwegian journalist
• Hans Johnsen, American Medal of Honor recipient
• Harvey M. Johnsen, American federal judge
• Håkon Johnsen (1914–1991), Norwegian politician for the Labour Party
• James Roland "Jim" Johnsen, American university president
• Jarl Johnsen (1913–1986), Norwegian boxer
• Jennie Johnsen (born 1977), Norwegian politician for the Liberal Party
• Johan Christian Johnsen (1815–1898), Norwegian politician
• John Johnsen (1892–1984), Norwegian freestyle and backstroke swimmer
• Julia Emily Johnsen (1881-1971), American author and editor
• Justin Meldal-Johnsen (born 1970), bassist with the artist Beck
• Ketil Melsted Johnsen Motzfeldt (1814–1889), Norwegian Minister of the Navy and Minister of Postal Affairs
• Lárus Johnsen (1923–2006), Icelandic chess master
• Linda Johnsen (born 1954), American author on yoga and Hinduism
• Marius Johnsen (born 1981), Norwegian footballer
• Michael Johnsen, Australian politician
• Nikolai Johnsen (born 1988), Norwegian television personality
• Olaus Johnsen, World War I pilot
• Pål Johnsen, Norwegian hockey player
• Per Johnsen, Norwegian sprint canoeist
• Peter Johnsen, American educator at Bradley University
• Robert Johnsen (1896–1975), Danish gymnast, 1920 Summer Olympics
• Ronny Johnsen (born 1969), Norwegian footballer
• Sigbjørn Johnsen (born 1950), Norwegian politician for the Labour Party
• Steinar Sverd Johnsen, Norwegian musician and composer
• Theo A. Johnsen (1857–1911) American manufacturer of ski equipment
• Tor Gunnar Johnsen, Norwegian footballer
• Torhild Johnsen, Norwegian politician for the Christian Democratic Party
• Vibeke Johnsen, Norwegian team handball player
• Wayne Johnsen (born 1977), American boxer

• Castle Bryant Johnsen, television computer artistry group
• Peter Johnsen Rooming House, near Sycamore, Illinois
• Jensen (surname)
• Jenson (name)
• Jonsen
• Jonson