The research reported in this dissertation centers around John Irwin's recent book, The Jail: Managing the Underclass in American Society (1985)', and provides a data informed critique of his study. It examined the records of people booked and incarcerated in jails varying in size and other characteristics in order to evaluate Irwin's conclusions that were made from his study of inmates at one jail in San Francisco County, California. The research portion of this dissertation was a comparative study of six Northwest jails in Multnomah County, Oregon and Skamania County, Washington and the varying characteristics of 1,306 jail prisoners incarcerated in them. Drawing upon inmate records, it was possible to obtain a charge distribution of the population selected for study as well as pertinent findings on other variables of age, gender, race, location, time incarcerated in the six detention locations, and disposition of charges. Most important to this study was the issue of crime severity for which a Statutory Seriousness Scale (SSS) was designed. The scale was based on the revised codes (criminal laws) of Oregon and Washington. Irwin put forth the argument that jails are occupied predominantly by a rabble class of inmates who have committed mostly petty crimes or no crimes at all. He defined the rabble class as those who are detached and disreputable persons who do not fit into conventional society and are irksome and offensive lower class members. It is not so much Irwin's definition of rabble that is at issue, rather, it is his contention that the nation's jails are populated predominantly by persons whose "crime" is that they are "offensive," rather than lawbreakers involved in serious criminal acts. According to Irwin, the primary function of the police is to manage, by various means, this disreputable underclass. The data gathering procedures used by Irwin were not entirely satisfactory, casting doubt on the accuracy of his claims. Accordingly, additional inquiry into jail populations is in order. The data uncovered in the present study suggests that, contrary to Irwin's thesis, many people arrested, booked, and jailed as a result of committing fairly serious crimes. This conclusion was true for the six jails and the 1,306 persons whose records were studied. The research suggests that Irwin's argument is not true for jails everywhere and that jails here do not seem to be filled mainly with persons whose primary problem is their offensive behavior. Instead, jails house a majority who have committed fairly serious acts of lawbreaking.