1840 was the last US Census that provided limited information. Below is the 1840 Fulton County, Illinois census for my great great great great grandfather, Henry Emery.
A key problem with this census is that it fails to list the names of other members living in the household. You have to do some detective work to figure out whether you have the right family. Relying on the book "Conrad Emery and His Descendants", written by Frederic B. Emery helped verify where the Emery family was living in 1840.
According to the 1840 Census, there were 9 family members living in the household. While I do not know whether the census was taken at the beginning of the year or the end of the year, this particular census would seem to match the number of family members in the Emery household.
In addition to Henry, wife Olive (Jacobs), their 7 children at the time were Mary, Amelia, David (my great great great grandfather), James, Elizabeth Celia, John and Edith Caroline.
Page 2 (Henry Emery family total is 3rd from the bottom)
I notice on line 5 is another Emery, which looks like "David" (my great great great great great grandfather), most likely Henry's father who moved to Fulton County on October 16, 1834.