Free People of Color (generally African-American) were either freed (manumitted) slaves, former slaves who'd purchased their freedom, or persons born free but required to register in Slave States (including DC) and carry "free papers" at all times.
Please use the Free People of Color category at the state level for individual profiles.
From the colonial to post-slavery period, people were classified by governmental and social institutions. While the official census classifications varied, in general, White, Negro or Black, Mulatto, Indian and sometimes Chinese were the norms. People classified as Indians, particularly after the last of the Indian Removals (particularly the Cherokee Removal aka The Trail of Tears) were also frequently suspected of being Negro or Mulatto, and thus subject to the same suspicions as Free People of Color (though Indians were technically separate).
Slave Codes, Poll Taxes and laws limiting educational opportunities, applied to 'Negro, Mulatto, Mustee' individuals, all considered to be People of Color, despite being legally free (DC's Black Codes particularly insidiously set curfews which applied to both enslaved and free people judged to be 'of Color' by local constables).
These classifications appear in newspapers, legal documents, etc, and were used to enforce various codes in all states, costing people jobs, homes and more.
Resources
The Indians of North Florida timeline describing varied relationships between races in the South
National Humanities Center on Free Born African Americans and Identity
Woodson, Carter G., Free Negro Heads of Families in the United States in 1830 Washington DC: The Association for the Study of Negro Life and History, Inc., 1925
The Journal of Negro History. Coverage: 1916-2001 (Vols. 1-86) Association for the Study of African American Life and History, Inc. (only Volumes through 1922 are free)
Race, Slavery, and Free Blacks Series II: Petitions to Southern County Courts: