The Duchy of Samogitia (Žemaičių seniūnija, Księstwo żmudzkie) had been the administrative unit of the Grand Duchy of Lithuania from 1219 (and from 1569, a part of the Polish-Lithuanian Commonwealth). From 1419 to 1441 it was known as Eldership of Samogitia. Grand Duke of Lithuania had the title of a Duke of Samogitia, although the actual ruler of the province, responsible to the Duke was known as general starost (elder) of Samogitia.
The Duchy was located in the western part of the present Republic of Lithuania. Historically, its western border had been a Lithuanian border with the Baltic Sea; in the north, it bordered the Duchy of Courland and Ducal Prussia in the south. During the Middle Ages and until partitions in 1795, Samogitia had clearly defined borders as Duchy of Samogitia, later the understanding of it changed slightly as it was associated with the Samogitian Diocese. Nowadays Samogitia is mainly associated with the ethnographic region and is not defined administratively.
Samogitia is a Latinized version of the name Žemaitija, meaning "the Lowlands" as opposed to Aukštaitija for "the Highlands". In the Middle Ages, the names Samaiten, Samaitae, Zamaytae, Samogitia, Samattae, Samethi were used in German and Latin sources. They, together with other variants Schmudien, Schamaiten (German) and Żmudź (Polish), are all derived from the Lithuanian Žemaitija.
The Duchy was located in what today is several counties (apskritis) in Lithuania: a small part of Kaunas County (Kauno Apskritis), the western part Šiauliai County (Šiaulių Apskritis), Tauragė County (Tauragės Apskritis), Telšiai County (Telšių Apskritis), the northern part of Klaipėda County (Klaipėdos Apskritis) and the northern part of Marijampolė County (Marijampolės Apskritis).
The major part of Samogitia is located on Western Upland. Lowlands which are referred in its name are on the border between Samogitia and Eastern Lithuania, along the Nevėžis River.
Duchy of Samogitia had the size of approximately 25 700 square kilometers.
Since the formation of the Grand Duchy of Lithuania in 13th century, Samogitia was its dependent territory, however sometimes the influence of the Lithuanian Grand Duke was very limited. During the rule of the first Lithuanian king, Mindaugas, Samogitians pursued an independent foreign policy and continued fighting with the Knights of the Sword even after King Mindaugas had signed a peace treaty with them.
Samogitia for 200 years played a crucial role in halting the expansion of the Teutonic Order and defeated the Knights of the Sword in the Battle of the Sun (1236) and the Livonian Order in the Battle of Skuodas (1259), and the Battle of Durbe (1260).
In the atmosphere of fierce battles with the Teutonic Knights, the Lithuanian rulers Jogaila and Vytautas several times ceded Samogitia to the Teutonic Order in 1382, 1398 and 1404. However, the Teutonic Knights were not very successful in subjugating the land, and Samogitians revolted in 1401 and 1409. After the defeats in the Battle of Grunwald (1410) and following wars, in 1422 the Teutonic Order ceded Samogitia to the Grand Duchy of Lithuania under the Treaty of Melno.
The Grand Duke of Lithuania Casimir Jagiellon acknowledged the autonomy of Samogitia in the Grand Duchy of Lithuania and then issued a privilege to the Eldership of Samogitia to elects its own elder (starost) in 1441.
Because of its prolonged wars with the Teutonic Order, Samogitia had developed a social and political structure different from the rest of Lithuania. It had a larger proportion of free farmers and smaller estates than in Eastern Lithuania.
As with most of the Polish-Lithuanian Commonwealth, Samogitia has suffered in the aftermath of the Swedish invasion of Poland (the Deluge, mid 17th century). Its population has dropped from close to 400,000 to about 250,000; only to return to 400,000 by the late 18th century.
After the annexation of Lithuania by Imperial Russia, Samogitia was included in the Vilna Governorate; in 1843 it was transferred to a newly established Kovno Governorate. At the beginning of the 19th century Samogitia was the center of Lithuanian national revival, which stressed the importance of the Lithuanian language and opposed russification and polonization attempt.