De Geer (also: De Geer van Jutphaas and De Geer van Oudegein) is a family of Walloon origin that belongs to the Swedish and Dutch nobility.
The name is derived from the town of Geer near Liège). The oldest known ancestor is Lambier de Geer, lord of Gaillarmont, who died in 1399 in Liège. His descendant Louys de Geer (1535-1602) moved from Liège to Aachen and later to Dordrecht in the Dutch Republic for religious reasons. Next generations became notable in Sweden and the Netherlands from the early 17th century, mainly centered on the iron foundry company town Finspång, but often extending to science, art and national politics. The larger, Swedish branch of the family retained its contacts with the Netherlands. Some of them hold the title baron. Both branches are still in existence and continue to thrive.
Notable members in selection
- Louis de Geer (1587–1652), Dutch financier and industrialist, founder of the Swedish branch.
- Louis De Geer (1622–1695), industrial entrepreneur.
- Charles De Geer (1720–1778), Swedish entomologist.
- Charles De Geer (1747–1805), Swedish politician
- Emanuel De Geer (1748–1803), Swedish Council member
- Robert Wilhelm De Geer (1750–1820), Finnish lantmarskalk of the Noble estate at the Diet of Porvoo.
- Charlotta Aurora De Geer (1779-1834), Swedish salonist.
- Carl De Geer (1781–1861), Swedish lantmarskalk of the Riksdag of the Estates
- Jan Lodewijk Willem de Geer van Jutphaas (1784-1857), Dutch politician.
- Ulla De Geer (1793-1869), Swedish salonist.
- Barthold Jacob Lintelo de Geer van Jutphaas (1816–1903), Dutch jurist and historian
- Louis Gerhard De Geer (1818–1896), Swedish statesman and writer, Prime Minister of Sweden 1876–80
- Karl Vilhelm Konstantin De Geer (1839-1904), Finnish general in the Imperial Russian army 
- Gerhard Louis De Geer (1854–1935), baron, Prime Minister of Sweden 1920–21
- Gerard De Geer (1858–1943), Swedish geologist.
- Sten De Geer (1886-1933), Swedish geographer and ethnographer
- Dirk Jan de Geer (1870–1960), prime minister of the Netherlands.
- Willem De Geer (1927-1984), Swedish artist and portrait painter. Great-grandson of Louis Gerard De Geer.
- Carl Johan De Geer (1938-), Swedish artist.
- Ursul de Geer (1946-), Dutch actor, director and television producer.
- Boudewijn de Geer (1955-), Dutch football player, grandson of Dirk Jan de Geer.
- Jonas De Geer (1971-), Swedish nationalist and traditionalist Catholic writer.
- Mike de Geer (1989-), Dutch football player, son of Boudewijn de Geer.
- Nederland's Adelsboek 83 (1993), pp. 42-86.