ScotlandsPeople is the privately-run agency the Scottish government provides for public access to all their records. An initial browse to confirm an individual's existence in the census is free. There is a charge for all further information.
Ancestry.com's Original data: Scotland. 1871 Scotland Census. Reels 1-191 provided by General Register Office for Scotland, in Edinburgh, Scotland.
FreeCEN is a voluntary project conducted on a county-by-county basis. To check coverage by census year and county, go to http://www.freecen.org.uk/statistics.html.