Sir William Essex, 1st Baronet (c. 1575 – c. 1645), was an English politician who sat in the House of Commons between 1597 and 1601.
Essex was the son of Thomas Essex, of Bewcot, Berkshire, by Joan Harrison, daughter of Thomas Harrison.
In 1611 he was created a baronet, of Bewcot in the County of Berkshire.
During the Civil War he was in command of a parliamentary company of foot in a regiment commanded by his son, Charles Essex.
Sir William was taken prisoner at the Battle of Edgehill in 1642 while his son was killed in action.