What was in each census? For a look at each census year’s census questions, the official enumeration date, census maps, etc., visit year-by-year quick census facts.
A wide variety of options exist online for searching and viewing digitized copies of U.S. census records from 1790 to 1940 (the most recent census released to the public). Several subscription-based sites offer the entire run, with seamless searching and browsing. You can also achieve free access to the entire U.S. census run 1790–1940, however, if you are willing to use a combination of websites and put in a little extra effort. Using alternate sources for the U.S. census can also be helpful when you can't find an ancestor where you expect him to be through a particular site's search engine. It's also a good strategy for situations when you can't read a census image because it is blurry or faded. For efficient, thorough census research you will often want to use more than one source.
Sources for U.S. Census Records Online
Ancestry.com - U.S. Federal Census Collection (subscription required)
Subscribers to Ancestry.com can access the entire available run of U.S. census records, from 1790–1940, including available fragments of the destroyed 1890 census. A number of special census schedules are also included in this collection, including the 1850 and 1860 Slave Schedules, the 1890 Veterans Schedules, the 1880 Schedules of Defective, Dependent, and Delinquent Classes, 1850–1880 Mortality Schedules (plus 1885 state mortality schedules from Colorado, Florida, and Nebraska), and select U.S. Federal Census Non-Population Schedules, 1850–1880 (agricultural, industry/manufacturers, and social statistics).
FamilySearch.org - United States Census (free)
FamilySearch hosts free indexes to the U.S. census from 1790–1940, and also offers free access to digitized images for the years 1850, 1870–1880, and 1900, as well as 1940 (which is completely indexed except for Puerto Rico). Indexes for the other years are also linked to images, but on subscription-based partner sites: 1790–1850 (Ancestry.com, or free at local Family History Centers), 1860 (Fold3.com), 1890 (Ancestry.com), and 1910–1930 (Ancestry.com). In addition, FamilySearch provides access to the 1890 Veterans Schedules, the 1850 Mortality Schedules, the 1850 Slave Schedules, and the 1930 Census of Merchant Seamen (which states "index and images," but as of the time of this writing only provides an index).
Heritage Quest (free through subscribing libraries)
U.S. Federal Census records from 1790 through 1930 are available through HeritageQuestOnline.com, a subscription site available only through subscribing libraries, not individual subscription. Digitized images are available for U.S. censuses 1790–1940. This collection also includes indexes created by HeritageQuest, so you may get different results than through other commercially available census indexes; however, no index is available for 1830, 1840 or 1850, and partial indexes only are available for 1930 and 1940. Check with your local, state and/or university library to see if they offer access to HeritageQuestOnline; if so, most will provide remote access via your library card number.
Internet Archive - United States Census (free)
Internet Archive (Archive.org) has scanned the U.S. census 1790–1930 from microfilm from the collections of the Allen County Public Library, originally from the United States National Archives Record Administration. This is an alternative, sometimes clearer, scanning of U.S. census images and is completely free for browsing. These are digitized images only, with indexes not available. See Making the Most of Internet Archive for details on other available genealogical records.
FindMyPast.com (subscription or pay-per-view)
Brightsolid, the company behind the popular UK website FindMyPast.co.uk, has also entered the U.S. market with FindMyPast.com, and the companion site CensusRecords.com. Both will eventually offer indexes and images to the entire run of available U.S. census records on both a subscription and a pay-per-view basis. You can view available records under their "Pay As You Go" page, which currently includes indexes and transcriptions for 1790–1930, with the exception of the surviving 1890 census schedules. Images are currently available for all years 1790–1930. The 1940 Census is also available, with free access, on FindMyPast.com.
Need to KnowWhen You Need an Alternate Image
FamilySearch.org is the original source of the majority of digitized U.S. census images on FamilySearch, Ancestry.com, and FindMyPast.com. Thus, you'll generally find the same image on each site. HeritageQuest (free through participating libraries) did its own scanning of U.S. census records, which provides an alternative digital version when you encounter an unreadable image. Internet Archive (free, but browsable only) also offers alternative images (some of the clearest in my opinion), digitized from microfilm at the Allen County Public Library.
When You Want 100% Free Access
As mentioned previously, Heritage Quest Online offers free access to all U.S. census images 1790–1940 (and select indexes) to anyone who has free access through a participating local, state, or university library system. Alternatively, you can use the free indexes available on FamilySearch.org, in combination with the free digitized U.S. census images on Archive.org to achieve free access to the entire U.S. census collection 1790–1930. The 1940 U.S. census is completely free from several sources, including Archives.com (not to be confused with Internet Archive - archive.org), Ancestry.com (free account required to view records), FamilySearch.org, MyHeritage.com, and FindMyPast.com (free registration required). Archives.com, FamilySearch.org and FindMyPast.com share the same index, created by volunteer indexers through the 1940 US Census Community Project. Ancestry.com and MyHeritage.com have each developed their own, independent indexes.