Baldwin IV (1108 – 8 November 1171) was count of Hainaut from 1120 to his death.

Baldwin IV was the son of Count Baldwin III of Hainaut and Yolande de Wassenberg.^[1] Also known as Baldwin the Builder, he purchased the property of Ath in 1158 and built the Burbant tower. He ceded the locality of Braine-la-Willotte, also known as Braine-le-Comte, to the chapter of Sainte-Waudru in 1158. In 1159, he incorporated the seigniory of Chimay and in 1160 the châtellenies of Valencians and of Ostrevent.

Baldwin IV married Alice,^[1] heiress of Namur, and had the following children:

• Yolande (1131–1202), married first to Ivo II, Count of Soissons,^[1] and second to Hugh IV, Count of St Pol^[1]
• Baldwin (1134–1147)
• Agnes (1142–1168), married Ralph I, Lord of Coucy^[1] and had children including Yolande de Coucy, wife of Robert II, Count of Dreux.^[2]
• Geoffrey, Count of Ostervant (1147–1163), first husband of Eleanor, Countess of Vermandois
• Lauret(t)a (1150–1181), married first to Thierry of Alost,^[3] and second to Bouchard IV, Count of Montmorency^[4]
• Baldwin V (1150–1195),^[3] also count of Flanders by his marriage to Margaret I of Flanders.