The demography of Liverpool is officially analysed by the Office for National Statistics. The City of Liverpool together with the Metropolitan Borough of Sefton, the Metropolitan Borough of Knowsley, the Metropolitan Borough of St Helens and the Metropolitan Borough of Wirral forms the metropolitan county of Merseyside. With a population of around 466,400, Liverpool is the largest settlement in the county, the largest in North West England, and the fourth largest in the United Kingdom.