Census records are one of the building blocks for genealogy research in the United States. Many researchers grab the names they need, the approximate age, and family members, and move on. However, a census can offer you a vast amount of information.
The first U.S. census was taken in 1790 and every ten years after that. The 1850 census was the first to list everyone in the household by name; before that only the head of the household was listed by name plus the number of males and number of females. The Wisconsin state census was like that until 1905. The 1890 census was burned--at least most of it was, including all of Wisconsin--and that was one of the reasons for the founding of the U.S. National Archives, to have a safe place to keep important documents of the government.
Generally, it is easiest to start with the most recent census available that the person you are looking for should appear in and then work your way back in time. More recent census records have more details and each of these data elements gives you clues to use as you work your way through the earlier records.
Don't forget to use the non-population schedules, such as Agriculture, Manufacturing, Mortality, and business or Products of Industry as it is sometimes called. Not all years of the non-population schedules are still available; the agriculture schedules for 1900 and 1910, for example, were destroyed by Congressional order. In Wisconsin, we are lucky to have the Farm Statistics Enumeration records, which act somewhat like the federal agriculture schedule.
On Microfilm:
Population: 1840, 1850, 1860, 1870, 1880, 1900, 1910, 1920
Agricultural: 1850, 1860
Manufacturing: 1860
Mortality: 1850, 1860, 1880
Products of Industry: 1860
Also on Ancestry.com & HeritageQuest
Population: Adds 1930 & 1940 to the above dates
On Microfilm
Also on Ancestry.com
On Microfilm:
Burnett County, 1923-1960
Pierce County, 1923-1960
Polk County, 1924-1960
Saint Croix County, 1924-1956