Karl Friedrich Eichhorn (November 20, 1781 - July 4, 1854), was a German jurist.
The son of Johann Gottfried, he was born at Jena. He entered the University of Göttingen in 1797. In 1805 he became professor of law at Frankfurt an der Oder, a post he retained until 1811, when he accepted the equivalent chair at Humboldt University, Berlin. On the call to arms in 1813 he became a captain of horse, and at the end of the war was decorated with the Iron Cross.
In 1817 he was offered the chair of law at Göttingen, and, preferring it to the Berlin professorship, taught there with great success till ill-health compelled him to resign in 1828. His successor in the Berlin chair having died in 1832, he returned there, but resigned two years afterwards. In 1832 he also received an appointment in the Ministry of Foreign Affairs, which, with his labours on many state committees and his legal researches and writings, occupied him till his death at Cologne.
Eichhorn was regarded as one of the principal authorities on German constitutional law. His chief work is Deutsche Staats und Rechtsgeschichte (Göttingen, 1808-1823, 5th ed. 1843-1844). In company with Savigny and JFL Göschen he founded the Zeitschrift für geschichtliche Rechtswissenschaft. He was the author of Einleitung in das deutsche Privatrecht mit Einschluss des Lehnrechts (Göttingen, 1823) and the Grundsätze des Kirchenrechts der Katholischen und der Evangelischen Religionspartei in Deutschland, 2 Bde. (ib., 1831-1833).