During the legal battles that followed the 1954 Brown decision, the de jure-de facto binary became the key legal distinction used to define the limits of school desegregation. In recent years, historians have labeled de facto segregation as an evasive and misleading "myth." However, the concept had a long political career before it became a subterfuge. In fact, civil rights activists first invented the concept in an attempt to force legal recognition of segregated schools outside of the South. But in an ironic turn of events, school officials, judges, lawmakers, journalists, and ordinary citizens later appropriated the phrase to deny responsibility for the color line. Thus, what began as an allegation of racial discrimination ultimately became an impenetrable defense of legal innocence. This article recovers the decade of fierce public debates surrounding northern school desegregation by tracing the evolution of de facto segregation from allegation to defense to myth.