Censuses have been taken every 10 years since 1801 after the Census Act of 1800 paved the way for them to be taken.
The first four 1801/1811/1821/1831 were limited in nature and although the collection books may have contained names, the purpose of the censuses was to get statistical totals, so this information was in general destroyed soon after it was taken, leaving only some summary totals. I a very few cases, it is reckoned less than one in one thousand, the enumerator kept thier original collection books and where these have been located they have in most cases found thier way into the archive of the county concerned, though some may be still be in private hands. For example Cumberland has Holme Cultram 1821, Isel 1811, Newton Reigny 1821 and Skelton 1821. Westmorland only has this collection data for Beetham 1801 and 1811, and Crosby Ravensworth 1811. Unfortunately although they are known to exist thier current location is unknown. For further information check the Family History website, which has full details. Futher information is available in a book published by the University of Essex and available at Census Schedules.
The 1841 census is a bit limited in content and you should be aware that the age of anyone over 15 should be rounded down to the nearest multiple of 5, so an 18 year old could be listed as 15, a 39 year old as 35 and so on, this needs to be taken into account when checking ages. The 1851 census is much better with a lot more details and ages should be accurate, always providing the person giving the information knew everyones age, they did not always know this. When details were given those who were illiterate or even in some cases those who were not, could verbally give details for the enumerator to write down, if they were not local then their accents could result in name or place names being incorrectly spelt
The 1881 census can normally be found free of charge because of the work done by the LDS Church, other Census records will normally only be available from paid websites or printed books. The CFHS for example has the 1851 census in printed booklets for each area for sale in the Publications Section.
As with all other records these census records on line will have been manually transcribed and will contain errors which may make it difficult to find people.
There are other psuedo-censuses, for example Window Tax and Hearth Tax records which go back prior to 1841, but these in general are not complete records and only cover a certain part of the population, or have significant gaps in them due to lost original copies.
Using the census.
Censuses have been taking in England and Wales every 10 years starting from 1841 (1941 was not taken due to the war but there is the 1939 register which is actually more comprehensive than the 1941 census would have been.). The different censuses contain different amounts of information and some are more valuable than others. They do all give useful information though including names, addresses and ages as well as family relationships at the same address. Because of the 100 year closure rule the census details are not released until 100 years has passed so only the censuses up to 1911 have currently been released.
It is useful to know the dates on which the census was taken as this can help pinpoint the year of birth a little more accurately.
There is one other quirk in the 1841 census, the age of everyone over 18 was meant to be rounded down to the nearest 5 years, so for example someone who was 24 would be shown in the census as 20. Not all enumerators followed this example though and exact ages are sometimes shown. The 1841 census also does not show the exact place of birth, only whether the person was born in the same county or not, in some cases it may also show if a person was born in another country, for example Ireland.
There were censuses prior to 1841 in various forms, in fact right back to the census at the time of the Domesday Book in 1086. From 1801 to 1831 although information was collected at a local level it was destroyed as soon as the statistics were extracted, so in general all that remains of those statistics are total numbers and there are no individual name details.
It was only with the passing of the Population act in 1840 that the new form for censuses came into being. There are actually three separate censuses for England and Wales, Scotland and Northern Ireland though from 1841 to 1901 the censuses are coordinated into one. For 1911 the Scottish Census is kept separate and is only available through Scotlands People.
The details of the various censuses taken in Cumbria are kept by the relevant records office, they are also available on line from various websites though you normally have to pay for access, the exception being the 1881 census which is available free at Ancestry - 1881 Census. Many county libraries will also allow you to access these records on line free of charge (other than the normal cost of using their computers).
There are also a few Census transcriptions at Freecen
You should also bear in mind that these censuses have been manually transcribed and the on line records do have errors in them, sometimes it can take some careful searching using different spellings to find the person you want. It is also not unusual for people to be missing, the reason for this could be anything from being out of the country, through to errors and perhaps just not wanting to be on the census. So not finding someone in a census does not mean they did not exist. Also be aware that many people were illiterate and the entries were made by the enumerators, who could and often did make mistakes, for example if the person was not a local their accent could affect what the enumerator heard and he would write that down phonetically, that affects names as well as places.
Apart from on line records, the Cumbria FHS does have a range of extract booklets from the 1851 census available in its publications range.
There are other earlier censuses taken for various purposes such as window tax or hearth tax or constables' censuses. In general because these were taxation returns they do not have so much detail and many people who were not taxable are omitted from these records. Hearth Tax existed from 1663 to 1688 and Window Tax from 1696 to 1851.
However the records that remain are few (This is not a complete list and there may be others):