From Wikipedia: Freedom Suits

 Quite enterprise before the Dred Scott case.

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Freedom suits were lawsuits in the Thirteen Colonies and the United States filed by enslaved people against slaveholders to assert claims to freedom, often based on descent from a free maternal ancestor, or time held as a resident in a free state or territory.

The right to petition for freedom descended from English common law and allowed people to challenge their enslavement or indenture. Petitioners challenged slavery both directly and indirectly, even if slaveholders generally viewed such petitions as a means to uphold rather than undermine slavery. Beginning with the colonies in North America, legislatures enacted slave laws that created a legal basis for "just subjection;" these were adopted or updated by the state and territorial legislatures that superseded them after the United States gained independence. These codes also enabled enslaved persons to sue for freedom based on wrongful enslavement.

While some cases were tried during the colonial period, the majority of petitions for freedom were heard during the antebellum period in the border or the Southern United States. After the American Revolution, most northern states abolished slavery and were considered "free." The United States Congress prohibited slavery in some newly established territories, and some new states were admitted to the union as free states. The rise in travel and migration of masters with slaves between free and slave states resulted in conditions that gave rise to slaves suing for freedom. Many free states had residency limits for masters who brought slaves into their territory; after that time, the slave would be considered free. Some slaves sued for wrongful enslavement after being held in a free state.

Other grounds for suit were that the person was freeborn and illegally held in slavery, or that the person was illegally held because of being descended from a freeborn woman in the maternal line. The principle of partus sequitur ventrem, first incorporated into English colonial slavery law by a 1662 statute in Virginia, established that children's status was that of the mother. It was adopted into law by other English colonies, and the states of the United States.

In Saint Louis, Missouri records of nearly 300 petition cases have been found that were filed between 1807 and 1860, and in Washington, D.C. nearly 500 petition cases were filed in the same period. A large portion of cases, as much as one-third, either never went to trial or were settled out of court. In the early nineteenth century in St. Louis and in Washington, D.C., nearly half of the attorneys at the bar may have acted as counsel for slave petitions.