Cornelia van Lalaing (1545 - 1610), was a Dutch noblewoman, famous for the role she played in the so-called "Rennenberg Treason" in 1579 during the Eighty Year's War.
She was the sister of George de Lalaing, count of Rennenberg, governor of Friesland, Groningen and Overijssel.
Her family was Catholic, but originally supported the Protestant House of Orange-Nassau.
the Prince of Orange, and his sudden and unexpected shift of side to the Catholics attracted great attention and became known as the "Rennenberg Treason".
Cornelia van Lalaing visited her brother in 1579, and allegedly convinced him to change sides.