General William Grinfield (c.1744/45–19 October 1803) was a British Army officer who served during the French Revolutionary and Napoleonic Wars. Grinfield joined the 3rd Regiment of Foot Guards in 1760 and was promoted through the ranks, becoming a major in the regiment in 1786. In 1793 his regiment joined the Flanders Campaign, fighting at the siege of Valenciennes and Battle of Lincelles, during which time he was promoted to lieutenant-colonel. Having held a higher army-wide rank than he did regimental rank, Grinfield was promoted by seniority to major-general later in the same year.