| William II | |
| Noble Family: | House of Avesnes |
| Father: | William I, Count of Hainaut |
| Mother: | Joan of Valois |
| Spouse: | Joanna, Duchess of Brabant |
| Birth Date: | 1307 |
| Death Place: | Warns, near Stavoren |
William II (1307 – 26 September 1345) was Count of Hainaut from 1337 until his death. He was also Count of Holland (as William IV) and Count of Zeeland. He succeeded his father, Count William I of Hainaut. While away fighting in Prussia, the Frisians revolted. William returned home and was killed at the Battle of Warns.
William was born in 1307, the son of William I of Hainaut and Joan of Valois.
In 1334, he married Joanna, Duchess of Brabant, the daughter and heiress of John III, Duke of Brabant, but had no issue.
He fought in France as an ally of the English (he was the brother-in-law of King Edward III of England). In 1339, William participated in the Siege of Cambrai (1339). In 1345, two months before he died, he, because the bishop, John van Arkel, was trying to regain the bishopric's historical independence from Holland.
William fought against the Saracens, and went on crusade with the Teutonic Order in Prussia. He was killed near Stavoren, during one of the battles of Warns against the Frisians in 1345.
William was succeeded by his sister, Margaret of Hainaut, who was married to Louis IV, Holy Roman Emperor. Hainaut, Holland and Zeeland became a part of the imperial crown domains.