Johannes Hillmann (1881–1943) was a German teacher, botanist, and lichenologist.
Hillmann researched lichens from the period 1916 to 1943, contributing 36 publications on the subject.
He is perhaps best known for his contributions to the families Parmeliaceae and Teloschistaceae, which were published in Gottlob Ludwig Rabenhorst's influential work Dr. L. Rabenhorst's Kryptogamen-Flora von Deutschland, Oesterreich und der Schweiz.
His herbarium of specimens, located in Buckow, was destroyed during World War II.
[1] Four lichen species named after Hillman are Buellia hillmanii Erichsen (1930), Lecidea hillmannii Anders (1922), Micropeltella hillmanniana Kirschst.