This essay suggests, in five topics, that America’s one-drop rule of invisible Blackness arose in the North between 1830 and 1840. A Bidirectional Strategy describes the analytic approach of bracketing the date by working forwards in time from the Revolution and backwards from Jim Crow. Journals and Diaries presents evidence from travelers’ accounts and newspaper advertisements to show that descriptive terminology changed from “white” to “white-looking” during this period. Literature and Drama shows that “passing” literature, which depends upon the one-drop rule for intelligibility, first arose in this period. Court Cases discusses four pivotal court cases from before and after the emergence of the one-drop rule—two in Ohio and two cases in Kentucky. Graphs and Charts presents graphs of court decisions to show how criteria for determining whether you were White or Black changed over the past two centuries.