Boulter's Lock is a lock and weir on the River Thames in England on the eastern side of Maidenhead, Berkshire. A lock was first built here by the Thames Navigation Commission in 1772. The lock is on the western side of the river between the main (A4094) Maidenhead to Cookham road and Ray Mill Island. The name is also used for the immediate surrounding area. The weir is some way upstream of the lock, at the northern end of Ray Mill Island.