Jacobus Deketh (or de Keth) (Harlingen, 1726 – Zeewijk (Almenum), 26 July 1764) was a captain in the Frisian Admiralty, one of the five admiralties of the Dutch Republic.
In 1744 at the age of 18, Deketh joined the Admiralty of Amsterdam.
He became a lieutenant and later extraordinary captain and sailed to the Dutch East Indies.
In 1758, Deketh continued his career in the Frisian Admiralty.
He became captain of a ship, Edam.
He was appointed full captain of the Frisian Admiralty in 1760.