Wilhelm Daniel Joseph Koch (5 March 1771 - 14 November 1849) was a German physician and botanist from Kusel, a town in the Rhineland-Palatinate.
Koch studied medicine at the Universities of Jena and Marburg, and afterwards was a Stadtphysicus (state physician) in Trarbach and Kaiserslautern (1798). In 1824 he became a professor of medicine and botany at the University of Erlangen, where he stayed for the remainder of his life. At Erlangen, he was also director of the botanical gardens. In 1833, he was elected a foreign member of the Royal Swedish Academy of Sciences.
Among his better written efforts was a synopsis on German and Swiss flora titled Synopsis florae germanicae et helveticae (1835-37). Another noteworthy publication of his was Catalogus plantarum florae palatinae (Catalog of Palatinate flora) (1814).
The plant genus Kochia (Chenopodioideae) is named in his honor.