The Colonial Office was a government department of the Kingdom of Great Britain and later of the United Kingdom, first created to deal with the colonial affairs of British North America but needed also to oversee the increasing number of colonies of the British Empire.
It was headed by the Secretary of State for the Colonies, known as the Colonial Secretary.
First Colonial Office (1768–1782)
Prior to 1768, responsibility for the affairs of the British colonies was part of the duties of the Secretary of State for the Southern Department and a committee of the Privy Council known as the Board of Trade and Plantations. 
In 1768 the separate American or Colonial Department was established, in order to deal with colonial affairs in British North America. With the loss of the American colonies, however, the department was abolished in 1782. Responsibility for the remaining colonies was given to the Home Office, and subsequently (1801) transferred to the War Office.
Second Colonial Office (1854–1966)
The War Office was renamed the War and Colonial Office in 1801, under a new Secretary of State for War and the Colonies, to reflect the increasing importance of the colonies. In 1825 a new post of Under-Secretary of State for the Colonies was created within this office. It was held by Robert William Hay initially. His successors were James Stephen, Herman Merivale, Frederic Rogers, Robert Herbert and Robert Henry Meade. 
In 1854, the War and Colonial Office was divided in two, and a new Colonial Office was created to deal specifically with the affairs in the colonies and assigned to the Secretary of State for the Colonies. The Colonial Office did not have responsibility for all British possessions overseas: for example, both the Indian Empire (or Raj) and other British territories near India, were under the authority of the India Office from 1854. Other, more informal protectorates, such as the Khedivate of Egypt, fell under the authority of the Foreign Office.
The increasing independence of the Dominions – Australia, Canada, New Zealand, Newfoundland and South Africa – following the 1907 Imperial Conference, led to the formation of a separate Dominion Division within the Colonial Office. From 1925 onwards the UK ministry included a separate Secretaries of State for Dominion Affairs were appointed.
In 1966, the Commonwealth Relations Office was re-merged with the Colonial Office, forming the Commonwealth Office. Two years later, this department was itself merged into the Foreign Office, establishing the Foreign and Commonwealth Office.
The Colonial Office List
From 1862, the Colonial Office published historical and statistical information concerning the United Kingdom's colonial dependencies in The Colonial Office List ,  though between 1926 and 1940 it was known as The Dominions Office and Colonial Office List .  It later became known as the Commonwealth Relations Office Year Book and Commonwealth Office Year Book . In addition to the official List published by the Colonial Office, an edited version was also produced by Waterlow and Sons.  It can be difficult to distinguish between the two versions in library catalogue descriptions. For example, The Sydney Stock and Station Journal of 3 December 1915 commented: 
This used to be the "Colonial Office Journal," but it looked – or sounded – too official, so they changed it to "The Colonial Journal." But it is still edited by Sir W. H. Mercer, K.C.M.G., one of the Crown Agents for the Colonies, but it is printed by Waterlow and Sons, London Wall. It comes as near to being an "Official publication" as possible, but we'll assume that it isn't.