Census Day
1790 to 1820--Census day was the first Monday in August
1830 to 1900--Census day was June 1st
1910--Census day was April 15th
1920--Census day was January 1st ( BRRRR!)
1930 to 1960--Census day was April 1st
Your Guide to the Federal Census by 
Map Guide to the U. S. Federal Censuses, 1790-1920 by Census Records have been copied, printed, microfilmed and digitized over the course of time. Each format has its own indexing system. Here's a brief entry guide to assist your search:
Online search: Use the search boxes available through either Heritage Quest or Ancestry.com. In most cases you can search by name. The online census covers 1790 to 1950 and is taken every 10 years. See our Genealogy Databases infoguide. (Ancestry.com Library Edition is only accessible IN your local library and not from home.)
For information on understanding the wards and municpalities used in the federal 1850 census of New Orleans, see the link below from the New Orleans Public Library:
The 1950 census is now available. Do you know how to find your ancestors? Key strategies are listed on the National Archives site.