The country of Hesse has had different boundaries at different times. The earliest inhabitants of the area were the Chatti, a Frankish (see Franks) tribe whom Tacitus describes and with whom the Hessi may be identified. The Hessians were converted to Christianity after the fall of the Roman Empire, mainly through the efforts of St. Boniface. Their land was included in the archbishopric of Mainz, and religion and culture were alike kept alive among them largely by the Benedictine abbeys of Fulda and Hersfeld.

As part of the Carolingian Empire, Hesse contributed also to the movement against the imperial power which followed the death of Charlemagne. The Hessian Conrad of the Franks was elected as Conrad I in 911, but on his death the crown passed out of Frankish hands to Herny of Saxony. From 1130 to 1247 Hesse formed part of Thuringia. [Much of the old architecture found today in the German cities of Fulda and Bad Hersfeld date to this period.] But on the death, childless, of the Thuringia ruler Henry Raspe in 1247 a conflict about the succession broke out; and Hesse was won by Sophie of Brabant for her son, Henry, the Child of Brabant. It thereupon became an independent landgraviate [1]. In 1292 Henry was raised to the rank of prince of the empire. The landgraves [2] were constantly at variance with the archbishop-electors of Mainz, who had possessions in Hesse. In the 15th century the country was twice divided among members of the ruling family, but no lasting division took place before the Reformation.

From 1509 to 1567, the difficult Reformation years, Philip the Magnanimous, the most famous of all Hessian rulers, was landgrave. A reformer in both senses of the word, he promoted the Protestant faith and cared for the education and general welfare of his country; in 1527 he founded the Protestant University of Marburg. On his death in 1567 Hesse was divided among his four sons into Hesse-Cassel, Hesse-Marburg, Hesse-Rheinfels and Hesse-Darmstadt.

Hesse-Cassel (later known also as Electoral Hesse) consisted of about half the former country and was apportioned to Philip's eldest son, William IV. A later ruler, Charles (1670-1730), is notable for being the first to adopt the system of hiring out his soldiers as mercenaries to help the national finances. As many as 22,000 Hessian troops later fought on the English side in the American Revolution. Charles also improved the prosperity of his land by bringing in the Huguenots.

After the American Revolutionary War, most of the Hessians found themselves stranded in America due to a lack of English military vessels to take them back to Germany; British troops recieving first priority. Privateers demanded exorbitant sums for transport. Thousands of Hessians deserted the idle British ranks, many changed their Germanic names to avoid reprisals, and melded into populations of the countryside to take up new lives. Some estimates are that thousands of Hessians thus became American citizens, most of them settling in the New York, New Jersey, and Pennsylvania areas.