William Baillie (died 1782) was a lieutenant-colonel in the East India Company's service. He was captured by Hyder Ali in 1780 at the Battle of Pollilur, and died in captivity in Seringapatam. Records in the India Office show that he entered the army of the East India Company on 18 October 1759 as a lieutenant in the infantry at Madras, and that the dates of his subsequent commissions were as follows: brevet-captain 5 September 1763, substantive captain 2 April 1764, major 12 April 1772, lieutenant-colonel 29 December 1775.