This fort is found in Kolkata, India. However, if you simply search for “Fort William” online, you will find that there is a town in Scotland with the same name. Regardless, for the purposes of this answer, I will be using information about the fort in Kolkata, India.
It was completed in 1780, and is one of the many forts that the British built in India when India was part of Britain. It covers about 70.9 hectares of land (or 175.19777 acres). It was used in the Battle of Plassey, which was a British victory over the French in India. The name comes from King William III of Britain, whom was in power between 1689 and 1702, and ruled over England, Scotland, and Ireland.