The first documented mention of Haigerloch was in the year 1095 on the occasion of the gift of the local castle. This castle was probably located in the area around the Upper Town. By 1200 the
Counts of Hohenberg appeared as the local lords and built a new castle on the Schlossberg. The lower town evolved into a market town.
Rudolf I, a brother-in-law of
Albert II Von Hohenberg-Haigerloch, awarded the town charter to Haigerloch before 1231. In 1268 a battle was fought just outside the city between
Zollern and Hohenberg. In 1291 the city was besieged by
Count Eberhard I of Württemberg; in 1347 the town was besieged again. From 1356 onward the upper town and lower town were administratively separated but were reunited when the lordship of Haigerloch was sold to Austria in 1381. The Habsburgs pawned the property on several occasions, including to the Counts of Württemberg. In 1487 rule of the city fell to the
Hohenzollern. In 1567 under
Christoph von Hohenzollern-Haigerloch the area around Haigerloch was an independent territory within the area of the
Holy Roman Empire as
Hohenzollern-Haigerloch. In this period, the present castle complex was built on the Schlossberg as the residence of the counts of Hohenzollern-Haigerloch, replacing the former high-medieval structure. In 1634 rule of the city descended to the line of
Hohenzollern-Sigmaringen, whose residence city was the city of Haigerloch between 1737 and 1769. In the last months of
World War II, Haigerloch was the location of the Kaiser Wilhelm Institute of Physics, part of the
German nuclear programme, which had the goal of achieving practical use of
nuclear fission. According to contemporary views, the
atomic bomb was not a direct objective of this work, but initially only the construction of the
Haigerloch research reactor, which was constructed in a beer cellar beneath the palace church. Through courageous negotiations by the pastor to rescue the reactor facility it was spared from demolition by an American command on April 24, 1945, and today is the site of the '''' with a replica of the reactor. ==Politics==