The first census in England and Scotland took place 1801, and 1841 in Ireland. The estimations of population size before those years are based on information on the number of baptise, weddings and burials that occurred every year. A census was arranged every tenth year with exception of 1941 when its was cancelled because of the Second World War.

The kingdom of Great Britain was created 1707 when England and Scotland were united. The British monarchy also included Ireland, which 1801 joined Great Britain to create the United Kingdom (UK). Most of Ireland became independent 1922 and only the Northern part remained in the union with Great Britain. The combined population of the three self-governing islands Isle of Man, Jersey and Guernsey are recorded here as "the Isles".

* = From 1922 only Northern Ireland.
** = Isle of Man, Jersey and Guernsey.

The population of Ireland increased rapidly during the first half of the 19^th century and numbered 8,3 million inhabitants 1846. But the Irish were completely dependent on potatoes as food and when the harvest failed in the late 1840:s a million Irishmen died of starvation. The reduction of the population continued during next hundred years because of emigration to America.