Today, an estimated 5400 people are civilly committed under state and federal sex offender programs. This Note surveys these civil commitment regimes and finds that seventeen jurisdictions (sixteen states and the federal government) have enacted legislative schemes that authorize the indefinite civil detention of people charged with, or previously convicted of, sex offenses to prisons or prison-like facilities—often for their entire lives. By charting the pervasiveness of sex offender civil commitment to prison, this Note provides new evidence that these sex offender civil commitment statutes are, in fact, punitive and, therefore, unconstitutional. Moreover, this Note argues that the Supreme Court’s decision in Kingsley v. Hendrickson calls into question the Court’s logic in upholding sex offender civil commitment regimes in prior cases. Traditionally, civil commitment jurisprudence has turned on whether the legislature intends to punish—not merely confine—sex offenders. Kingsley, however, suggests that confinement may be found punitive based solely on the objective harshness of the conditions of incarceration, regardless of whether any state actor intended for the conditions to be punitive. If incarceration conditions may now constitute punishment regardless of governmental intent, it follows that the government may be punishing thousands of sex offenders without authorization. Indeed, as this Note shows, convicted prisoners and committed sex offenders commonly experience identical conditions of confinement.