Humboldt University is in most cases likely to refer to the Humboldt University of Berlin (in German Humboldt-Universitt zu Berlin), the oldest university in the city of Berlin and from its founding in 1810 until 1949 known as the Friedrich Wilhelm University (Friedrich-Wilhelms-Universitt).
There is also a Humboldt State University in Arcata, California, about 300 miles north of San Francisco, known by this name since 1974.