If you have read some of my previous posts or know me personally then you already know that I love census records. Great place to start if you are looking for information. You still have to follow up on all the information contained therein but what a slice of history to peruse.
The census records for Great Britain, and yes Scotland is part of that entity, were taken on the following dates (Sunday/Monday except for 1939).
1801 thru 1831 - statistical information only. Usually households were not broken down or names etc. given. There is some debate as to the dates for the 1801 census but the other 3 were taken on the last weekend of May.
1841 - 06/07 June
1851 - 30/31 March
1861 - 07/08 April
1871 - 02/03 April
1881 - 03/04 April
1891 - 05/06 April
1901 - 31 March/01 April
1911 - 02/03 April
1921 - 19/20 June (will be available next year at some point. Still covered by 100 year privacy law)
For other dates and some concise information about what was included in each census visit http://www.talkingscot.com/censuses/census-dates.htm