Henry Casimir II of Nassau-Dietz (Dutch: Hendrik Casimir II van Nassau-Dietz; 18 January 1657 – 25 March 1696) was Stadtholder of Friesland and Groningen from 1664 till 1696.

Henry Casimir II of Nassau-Dietz was born in The Hague, the eldest son of Willem Frederik of Nassau-Dietz and Countess Albertine Agnes of Nassau, daughter of Frederick Henry, Prince of Orange, stadtholder of Holland, Zeeland, Utrecht, Guelders, and Overijssel.

When his father, a member of the branch of Nassau-Dietz, died in 1664, he was made stadtholder of Friesland and Groningen (under guardianship of his mother as he was then seven years old).

In 1675, Friesland voted to make its stadtholdership hereditary in the house of Nassau-Dietz.

Hendrik Casimir died in Leeuwarden, and was succeeded as stadtholder by his son Johan Willem Friso of Orange-Nassau.