The County of Mark (German: Grafschaft Mark, French: Comté de La Marck colloquially known as Die Mark) was a county and state of the Holy Roman Empire in the Lower Rhenish–Westphalian Circle. It lay on both sides of the Ruhr River along the Volme and Lenne rivers.
 The Counts of the Mark were among the most powerful and influential Westphalian lords in the Holy Roman Empire. The name Mark is recalled in the present-day Märkischer Kreis district in lands south of the Ruhr in North Rhine-Westphalia, Germany. The northern portion (north of the Lippe river) is still called Hohe Mark ("Higher Mark"), while the former "Lower Mark" (between the Ruhr and Lippe Rivers) is for the most part merged in the present Ruhr area.
 The County of the Mark enclosed an area of approximately 3,000 km2 and extended between the Lippe and Aggers rivers (north-south) and between Gelsenkirchen and Bad Sassendorf (west-east) for about 75 km. The east–west flowing Ruhr separated the county into two different regions: the northern, fertile lowlands of Hellweg Börde; and the southern hills of the Süder Uplands (Sauerland). In the south–north direction the southern part of the county was crossed by the Lenne. In the region of the Lower Lenne was the County of Limburg (1243–1808), a fiefdom of Berg.
 The seat of the Counts of the Mark von de Marck or de la Marck was originally the Burg Altena in the Sauerland region, but moved to Burg Mark near Hamm in the 1220s. The county was bordered by Vest Recklinghausen, the County of Dortmund, the Bishopric of Münster, the County of Limburg, Werden Abbey, and Essen Abbey.
 The coat of arms of the county was "Or a fess chequy Gules and Argent of three". These arms have been used by the city of Hamm since 1226. Many other places in the area include the red and white checkered fess in their arms as a reference to the county and often to their founders.
 Originally belonging to a collateral line of the counts of Berg at Altena, the territory emerged under the name of Berg-Altena in 1160. About 1198 Count Frederick I purchased the Mark Oberhof, a parish land (Feldmark) on the territory of the Edelherren of Rüdenberg, liensmen of the Cologne archbishop Philip von Heinsberg. Here Frederick had the Mark Castle (Burg Mark) erected as the residence of the new "Counts of the Mark". The nearby town of Hamm was founded by his son Adolf I, Count of the Mark in 1226, it soon became most important settlement of the county and was often used as residence.
 In the 1288 Battle of Worringen, Count Eberhard II fought on the side of Duke John I of Brabant and Count Adolph V of Berg against his liege, the Cologne archbishop Siegfried II of Westerburg, titular Duke of Westphalia. As Brabant and its allies were victorious, the County of Mark gained supremacy in southern Westphalia and became independent of the Archbishopric of Cologne. The territory of Mark was for long restricted to the lands between the Ruhr and Lippe rivers ("Lower Mark"). New territories in the north ("Higher Mark") were gained during the 14th century in wars against the Prince-Bishopric of Münster.
 In 1332 Count Adolph II married Margarete, the daughter of Count Dietrich VIII of Cleves. Adolph's younger son Adolph III upon the death of Dietrich's brother Count John acquired the County of Cleves on the western banks of the Rhine in 1368. In 1391 Adolph III also inherited the Mark from his elder brother Engelbert III and united both counties as "Cleves-Mark" in 1394.
 In 1509 the heir to the throne of Cleves-Mark John III the Peaceful married Maria, the daughter of Duke William IV of Berg and Jülich. In 1511 he succeeded his father-in-law in Jülich-Berg and in 1521 his father in Cleves-Mark, resulting in the rule of almost all territories in present North Rhine-Westphalia in personal union, except for the ecclesiastical states. The dynasty of Jülich-Cleves-Berg became extinct in 1609, when the insane last duke John William had died. A long dispute about the succession followed, before the territory of Mark together with Cleves and Ravensberg was granted to the Brandenburg Elector John Sigismund of Hohenzollern by the 1614 Treaty of Xanten (generally accepted in 1666). It then became part of the Kingdom of Prussia after 1701.
 In 1807 the County of the Mark passed from Prussia to France in the Treaties of Tilsit. In 1808 Napoleon then gave Mark to the elevated Grand Duchy of Berg, which was divided into four departments along the lines of Napoleonic France. Mark was in the Ruhr Department until the collapse of French power in 1813, when it returned to Prussia.
 The Prussian administrative reform of 30 April 1815 placed Mark within Regierungsbezirk Arnsberg, Province of Westphalia. The Hohenzollern Prussian sovereigns remained Counts of the "Prussian County of the Mark" until 1918.
The "County of the Mark" has no official meaning anymore, but is used to informally refer to the region in North Rhine-Westphalia.
 The House of La Marck is a cadet branch of Berg dynasty. Another surviving line of the House of Berg (more senior but less prominent in European History) became counts of Isenberg, then count of Limburg and Limburg Styrum.
 To France by the 1807 Treaty of Tilsit, incorporated into Grand Duchy of Berg
 Circles est. 1500: Bavarian, Swabian, Upper Rhenish, Lower Rhenish–Westphalian, Franconian, (Lower) Saxon
 51°40′25″N 7°48′57″E﻿ / ﻿51.67361°N 7.81583°E﻿ / 51.67361; 7.81583