Suburban Cook County was split away from Chicago, and 96 counties outside the collar counties were separated into 20 urban and 76 rural areas. Data were examined in two ways: (1) to determine the nature of growth in violent index offense arrests; and (2) to look at proportional changes in violent index offense arrests. Study findings showed that violent index offense arrests increased by 72 percent in urban counties and by 38 percent statewide between 1985 and 1991. Arrests for rape declined during the 6-year period in Chicago. Arrests for murder and robbery decreased in rural counties, while arrests for all types of violent index offenses increased in suburban Cook County, collar, and urban counties. Chicago, suburban Cook County, and collar and rural counties accounted for a smaller proportion of violent index offense arrests in 1991 than in 1985. Substantial increases occurred in the proportion of violent index offense arrests in urban counties for murder (up 4 percent), rape (up 9 percent), and assault (up 4 percent). Rural counties had proportionately fewer arrests for all violent index offenses except rape in 1991 than in 1985. 12 figures