Fort William is a British Raj fort in the Indian city of Calcutta and was named after King William of Orange.

The original fort was built by the British East India Company in 1696. A guard room in the fort was later named the infamous black hole of Calcutta.

A new fort was started by Robert Clive after the Battle of Plassey and was completed by 1780. It is octagonal with three sides facing the Hoogli River.