The Census Act 1800 also known as the Population Act 1800 (citation 41 Geo. III c.15) was an Act of the Parliament of Great Britain which enabled the first Census of England, Scotland and Wales to be undertaken. The census was carried out in 1801 and every ten years thereafter. The 1801 census estimated the population of England and Wales to be 8.9 million, and that of Scotland was 1.6 million. Ireland was not included in the census until 1821.
The first census of England had been carried out by William I and published in the Domesday Book in 1086. Various other censuses had taken place, such as that in the sixteenth century, in which bishops were asked to count the number of families in their dioceses. In the latter part of the eighteenth century, there were several proposals for a Census Bill and a growing concern about the population of Britain and its demand for food, particularly fueled by the publication, in 1798 of Thomas Robert Malthus's An Essay on the Principle of Population. The Census Bill was presented to Parliament on 20 November 1800, passed on 3 December and received Royal Assent on 31 December. The first census was held on Monday 10 March 1801.
Administration of the 1801 census 
The 1801 census was in two parts: the first was concerned with the number of people, their occupations, and numbers of families and houses. The second was a collection of the numbers of baptisms, marriages and burials, thus giving an indication of the rate at which the population was increasing or decreasing. Information was collected by census enumerators who were usually the local Overseers of the Poor or (in Scotland) schoolmasters. They visited individual households and gathered the required information, before submitting statistical summaries. The details of households and individuals were important only in creating these local summaries and were destroyed in all but a few cases. The idea of a census had been championed, amongst others, by John Rickman who was a clerk in the House of Commons. He subsequently undertook the analysis of the results and the preparation of abstracts and reports from the 1801 census (and the three following censuses).
Subsequent censuses 
The censuses held in 1811, 1821, and 1831 were based on the same model as the 1801 census. With the passing of the Population Act 1840, a new approach to censuses was adopted under the responsibility of the Registrar General and was first implemented in the 1841 census.