The United States is currently home to 5 percent of the world’s people and 25 percent of the world’s prisoners. African Americans and Latinos are disproportionately represented among America’s vast unfree population, with more black men under some form of carceral control (prison, parole, probation) than were enslaved in 1850. The systematic confinement and surveillance of people of African descent in the twenty-first century has led some scholars and activists to posit that contemporary mass incarceration is slavery, or, at the very least, an afterlife of slavery. In this telling, the carceral landscape of Mississippi cotton plantations and the antebellum slave patrol haunt contemporary super-max prisons and police departments empowered to detain, arrest, harass, and execute black bodies. This tragic narrative of American history points to enduring connections among police power, white supremacy, and black captivity. Yet, police power has also been indispensable to black liberation in the United States. The nineteenth-century abolition of slavery, post-Civil War Reconstruction (however brief), and the modern Civil Rights movement were all made possible by a vast expansion of the federal government’s police power. This talk explores the Janus-faced nature of police power in American history through the prism of nineteenth-century New York, where the gradual abolition of slavery coincided with the birth of the modern penitentiary. Well before the U.S. Civil War and the modern Civil Rights movement, New York’s state government deployed its police power to abolish chattel slavery and to build an expansive state prison system. Gradual emancipation liberated black New Yorkers from the yoke of chattel bondage, but structural racism rendered free people of African descent increasingly vulnerable to incarceration in penitentiaries that epitomized the carceral logic of liberal free-labor ideology.