I got this information from my good friend when I was first learning.
One of the most useful tools in research is the census. U.S. Federal Census began in 1790. The U.S. is the first country to have a federal census. Census were taken to determine how many representatives each state would receive. The census are available from 1790 to 1930. Each census year has a different information. The 1880 census was destroyed in a fire in Washington D.C.
When reading a census remember:
1. That the female head of household is not always the mother of the children listed.
2. Surname spellings may vary. Not everyone could read and write and many did not know the spelling of their name so the census taker spelled the name.
3. County lines changed with population and might have become part of a new state.
overview of census
1790 First time recorded- about 2/3 of the census survive today. Losses were in Del., Ky., Va., N.J., and Ga.
1830 First time census were sent to Washington D.C according to a law passed by Congress.
1840 Shows veteran history
1850 First time every member of the household was recorded. Family relationships were not recorded. Be aware that children listed may not be children head of house. First time place of birth is recorded
1880 first time family relationships are recorded. Also, place of parents birth is recorded.
1890 census destroyed in fire. However, information can be gathered through tax, voting, phone directory records.
1900 census records for the first time immigration year, number of children born, number living, language spoken in home.
1910 census records military information, number of years married, naturalized or alien. First time Native Americans recorded in general census. Native Americans had other census.
1920 census records for firs time all states and territories. National origin recorded. Many country origins were difficult to identify by citizens because the world map had changed. For example citizen who emigrated from Prussia is now Poland.
1930 census records families with radios and value of home
This is just a basic summary of the census.
Also there are state census records. Many states had their own census for tax purposes. These census were recorded every ten years but different years than the federal census.