The Eastern Association of counties was an administrative organisation set up by Parliament in the early years of the First English Civil War.
In January 1644 committeemen of the Eastern Association gathered at the Bury Conference to discuss their concerns as regards the proposed New Model Army.
[1]: 191 As part of Parliament's efforts to improve the administration of its forces, the Parliamentarian militias of Essex, Hertfordshire, Norfolk, Suffolk, Cambridgeshire were established as the "Eastern Association" on 20 December 1642.
One of the units which first became part of the Association's force was a "troop of horse" (cavalry) raised by Captain Oliver Cromwell.
Later in the year, the Eastern Association forces moved into the south of England where the Parliamentarian armies under the Earl of Essex and Sir William Waller had suffered setbacks.
Four cavalry and four infantry regiments of the Eastern Association army were absorbed into the New Model, and became the pattern on which most of the other units were formed.
At the same time, the criticism of the Earls of Manchester and Essex resulted in the Self-denying Ordinance, which placed command of the New Model Army in the hands of professional soldiers.