The County of Hainaut (French: Comté de Hainaut; Dutch: Graafschap Henegouwen; Latin: comitatus hanoniensis), sometimes spelled Hainault, was a territorial lordship within the medieval Holy Roman Empire that straddled what is now the border of Belgium and France. Its most important towns included Mons (Dutch: Bergen), now in Belgium, and Valenciennes, now in France.
The core of the county was named after the river Haine. It stretched southeast to include the Avesnois region and southwest to the Selle (Scheldt tributary). In the Middle Ages, it also gained control of part of the original pagus of Brabant to its north and the pagus of Oosterbant to the east, but they were not part of the old pagus of Hainaut. In modern terms, the original core of Hainaut consisted of the central part of the Belgian province of Hainaut, and the eastern part of the French département of Nord (the arrondissements of Avesnes-sur-Helpe and Valenciennes).
Hainaut already appeared in 8th-century records as a Frankish gau or pagus, which included the Roman towns of Famars and Bavay. In the 9th century, if not earlier, it was also described as a county, which implies that it had a single count governing it. As with many counties of the region, there was apparently a 10th-century fragmentation of territories among different counts, which is difficult to reconstruct. A single large territorial county was given its more-or-less final form in 1071 that lasted throughout the middle ages.
For much of its existence Hainaut was a frontier territory, bordering upon the kingdom of France. From 843 it was part of the “middle kingdom” of Lotharingia. After about 925 Lotharingia was definitively attached to the eastern Frankish realm that would become the Kingdom of Germany. Hainaut and its neighbourhood remained an important frontier area, or “march”, during the High Middle Ages. Though it was part of the Holy Roman Empire, which ruled from what is now Germany, it was culturally and linguistically French and part of the Catholic Archdiocese of Reims. Like its neighbours such as the counties of Brabant and Flanders, it was frequently entangled in the politics of France.
The Counts of Hainaut were often rulers of other counties, including Flanders and Holland. Examples of such personal unions include the following:
In 1432, Hainaut, Holland and Zeeland joined Flanders, Artois, Namur, Brabant, Limbourg, and later Luxembourg, within the large agglomeration of territories in the Low Countries, belonging to the French House of Valois-Burgundy. This new state, the Burgundian Netherlands, was later inherited by the Habsburg dynasty.
In 1659 and 1678 southern Hainaut was acquired by France. The northern part continued to be part of the Habsburg Netherlands. Like much of that state, the northern part of Hainaut was absorbed into the First French Republic at the end of the Ancien regime but later became part of Belgium in 1830.