Frederick William Horn (August 21, 1815 – January 15, 1893) was a German-American immigrant, lawyer, politician, and Wisconsin pioneer.

He was educated in Berlin, at the Gymnasium of the Gray Friar, but did not graduate, and entered the military service of Prussia.

He made his residence in Michigan but traveled extensively through Illinois, Iowa, Missouri, and finally Wisconsin.

He arrived in Milwaukee, in the Wisconsin Territory, in 1840 and, in 1841, settled in Mequon, in what was then Washington County.

In 1842 Horn entered his first public office when James Duane Doty, Governor of the Wisconsin Territory, appointed him Justice of the Peace for Washington County.

He served as postmaster for Mequon, while he was residing there, was Register of Deeds for the county in 1846 and 1847, and served on the Ozaukee County Board of Supervisors In 1848, he ran for and was elected to the first session of the Wisconsin State Senate, running as an independent Democrat.