An ancestors job can tell you so much about their life. You can gain insight into their daily life, income, and social status. Where they worked can also explain why they moved from place to place. Work records contain a wealth of information, but finding them is not always easy.
Some of the best sources for determining your ancestor's occupation begin with the Census records. In 1850, the US Census schedule held details about a person's occupation. Before 1850, the only indication of an occupation was the industry the person worked in.
In 1880 the question is asked how many months the person was unemployed. In 1910, two columns described employment, and three columns assessed whether the person was an employer, employee, or self-employed.
City Directories - your ancestor's employment details often appear in the city directories. They may list the type of work as well as the employer. A small but growing collection of city directories can be found for free at www.familysearch.org. They are also accessible on the paid sites of www.ancestry.com and MyHeritage.com
Draft Registration - men who registered for the draft in WWI were asked for their trade and employer. The registration card requested both the name of the employer as well as their location. These records can be found on www.familysearch.org for free, www.ancestry.com, www.fold3.com each charge a fee for access.
Obituaries - sometimes you can find almost an entire life story in a well-written obituary. You may find information on how long they were employed and what their position was with the employer.
Pay close attention to where a person most recently worked, as you may find more documentation for your ancestor. Be sure to collect all the occupational clues you can across your ancestor's lifespan.