The official census date was the night of 6/7 June 1841. Information recorded for each person included place of residence, name, age (rounded down to nearest 5 years for those over 15), sex, occupation, and whether born in that county or not.
Ancestry.com citation Ancestry.com. 1841 Scotland Census [database on-line]. Provo, UT, USA: The Generations Network, Inc., 2006. Original data: 1841 Scotland Census. Edinburgh, Scotland: General Register Office for Scotland. Reels 1-151. General Register Office for Scotland, Edinburgh, Scotland.
Note: The census information for a number of parishes was destroyed. Check the information at Ancestry.com or Scotlands People for a listing of missing parishes.