A census has been held in Britain every ten years since 1801 (excluding 1941). The earliest censuses were simply headcounts of the population.
However, from 1841, the format expanded to record the names of everyone living in a household or institution, together with details of their:
The records are arranged geographically (by 'enumeration district') and then by household, making them very useful sources for finding out about the people who used to live in the farmsteads and townships you may be investigating. Using census records in collaboration with early Ordnance Survey maps can also help to show us how settlements have expanded and declined over time, and even help to pinpoint when they became abandoned. They are also a valuable source for tracing the decline and survival of the Gaelic language in Scotland.
Census records dating from 1841 - 1901 are widely available in local studies libraries, archives and in General Register Office in Edinburgh. They are also available on-line, via the Scotland's People website, though this site is geared towards family historians and it is difficult to search by place-names (this option is only offered for the 1881 census - for all others, you require a surname to search on).
Detailed census records for the last 100 years are not available for inspection, but statistical reports for all censuses should be available in local libraries.