William Henry Brewer (September 14, 1828 – November 2, 1910) was an American botanist. He worked on the first California Geological Survey and was the first Chair of Agriculture at Yale University's Sheffield Scientific School.
William H. Brewer was born in Poughkeepsie, New York and grew up on a farm in Enfield, New York. In 1848 Brewer attended Yale and began studying soil chemistry under Professors Benjamin Silliman and John Pitkin Norton. There, Brewer was a founding member of Berzelius, one of Yale's oldest "secret societies". In 1852 he graduated from the first class of the Sheffield Scientific School with a Bachelor of Philosophy degree and began teaching at the Ovid Academy in Ovid, New York. It was in Ovid where Brewer first befriended Presbyterian minister Laurentine Hamilton.
In 1855 Brewer travelled to Europe where he studied natural science under Professor Robert Bunsen at the University of Heidelberg in Germany. He then went to Munich to study organic chemistry under Professor Justus von Liebig. In 1857 Brewer went to Paris, France and studied chemistry under Professor Michel Eugène Chevreul. In 1858 Brewer returned to the United States and married Angelina Jameson, of Ovid, New York on August 14, 1858. In October, he was appointed professor of chemistry at Washington and Jefferson College in Washington, Pennsylvania. His wife later died in June, 1859.