The name Cumberland was applied by Lieutenant-Colonel Robert Monckton to the captured Fort Beausejour on June 18, 1755 in honour of the third son of King George II, William Augustus, Duke of Cumberland, victor at Culloden in 1746 and Commander in Chief of the British forces. The old Mi'kmaq name for the area was "Kwesomalegek" meaning "hardwood point".
Cumberland County was created on August 17, 1759. When the Township of Parrsboro was divided in 1840, one part was annexed to Cumberland County and the other part annexed to Colchester.
The dividing line between Cumberland and Colchester was established in 1840. In 1897, a portion of the boundary line between the Counties of Colchester and Cumberland was fixed and defined.