Census refers to the periodic, compulsory collection of detailed population and household data by the state, used extensively in legal, regulatory and policy contexts. In the UK, censuses are conducted under specific legislation (primarily the Census Act 1920 for England, Wales and Scotland, and the Census Act (Northern Ireland) 1969), while in Ireland they are carried out under the Statistics Act 1993. For legal practitioners, census data is a key evidential and planning tool. It informs equality and anti-discrimination analysis, human rights impact assessments, public law challenges, resource allocation, housing and education planning, and demographic evidence in litigation or consultation processes. Census statistics are frequently cited in judicial review, statutory interpretation involving “ordinary residence” or “household” concepts, and in assessing compliance with public sector equality and socio‑economic duties. Across England & Wales, Scotland, Northern Ireland and Ireland, the core concept and use of a census are broadly consistent, though timing, questions and enabling statutes differ. The confidentiality of individual returns, restrictions on disclosure, and criminal offences for non‑compliance or unlawful use of data are critical legal features for data protection, information governance and public law practitioners.