Adelaide of Holland, Countess of Hainaut (Dutch: Aleide (Aleidis) van Holland; c. 1230 – buried 9 April 1284) was a Dutch regent. She was a daughter of Floris IV, Count of Holland and Matilda of Brabant. She was also a sister of William II, Count of Holland and King of Germany. She acted as regent for her nephew Count Floris V during his minority.
On 9 October 1246, Adelaide married John I of Avesnes, Count of Hainaut. Like her mother, she was a patron of religious houses. Her religious interest is reflected in that three of her sons became bishops, and her one daughter became an abbess. She also insisted on a bilingual education for them.
Between 1258 and 1263, Adelaide was regent of Holland in the name of her nephew Floris V. She called herself Guardian of Holland and Zeeland (Tutrix de Hollandie et Zeelandie). After he came of age, she continued to advise him. She died in 1284 at Valenciennes, but in 1299, with the death of Floris' son John I, it was her own son John II who inherited Holland through her.
She gave Town privileges to Schiedam, which afterwards had the right to be called a city. In it she founded Huis te Riviere, which was then the second largest castle in Holland.
Jacob van Maerlant dedicated his first poem, Geesten, to Adelaide.
With John I, she had the following issue:
- John II, Count of Hainaut and Holland (1247–1304)
- Baldwin (born after 1247, lived in 1299)
- Joanna, abbess of Flines (died 1304)
- Bouchard, Bishop of Metz (1251–1296)
- Guy, Bishop of Utrecht (1253–1317)
- William, Bishop of Cambrai (1254–1296)
- Floris, stadholder of Zeeland and Prince of Achaea (1255–1297)