I assume that you are asking about the Populist movement of the late 1800s. This is the one that formed the People's Party in 1892.
For the most part, the people who joined this movement were farmers. They formed the nucleus of the Populist movement, which had actually gotten started with the creation of the Farmers' Alliance. These farmers tended to be from the West and the South oof the US.
It should be noted that the Populists had a hard time making headway in the South because of racial issues. When the Populists tried to reach out to black farmers, their coalition tore apart.