Abstract: Following the introduction of a religion question in the 2001 Census of England and Wales, and its inclusion in the two subsequent censuses of 2011 and 2021, multiple analyses have concluded that the strictly Orthodox Jewish population, known as haredim, has most likely been consistently and substantially undercounted on each occasion. Beyond technical concerns about enumeration accuracy, this is a pressing social problem since a high proportion of this community is young, lives in overcrowded conditions and is economically vulnerable. Previous attempts to investigate the nature of this suspected undercount have been focused on assessing missing individuals while assuming that haredi households have been enumerated accurately. Here, geographical information is used which takes advantage of the fact that, like many ethnic minority groups, the haredi population forms voluntary enclaves, presenting the possibility to directly compare detailed household counts at the postcode sector level held by the community, with equivalent data from the 2021 Census. In doing so, it is demonstrated that the assumption of accurate household enumeration is probably incorrect and that there is credible evidence to indicate that compared with community records, haredi households were undercounted by between 21% and 26% in the 2021 Census.
