Eustace II of Boulogne accompanied William I of England (the Conqueror) during the Norman Conquest in 1066 and fought on his side at the Battle of Hastings.
His son, Eustace III, was a major participant in the First Crusade with his younger brothers: Geoffrey and Baldwin (who later became King of Jerusalem).
The county reverted to the crown and was passed to Adelaide of Brabant, wife of William III of Auvergne.
Boulogne was attacked and besieged a number of times during the Hundred Years' War and repeatedly passed between the English and the French.
Boulogne remained part of France, except for a brief period of English rule under Henry VIII.