The analysis is based on Uniform Crime Report data supplied by the Department of State Police. It focused on 21 of the 83 counties in Michigan and on 3 aggregate groups: the 83-county State total, the 17 largest counties, and 66 remaining small counties. The number of reported offenses for the five most numerous Index crimes--burglary, larceny, robbery, aggravated assault, and motor vehicle theft--were analyzed along with corresponding juvenile and adult arrest data. For each data set three issues were explored: (1) the trend from 1972 to 1977 for crime and arrest rates, (2) similar patterns of crime and arrest data among the counties, and (3) the distribution of individual Index crime categories in terms of percentages of all Index offenses and arrests. The analysis of Index offenses found the crime rate to be on the decrease. Moreover, relative frequencies of various crime categories followed a similar pattern for most counties, with the exception of Wayne County. Juvenile arrest rates have decreased and adult arrest rates have increased during the past 6 years, and adult arrests were markedly higher than juvenile arrests for crimes against persons. Also, crime prevention and crime reduction efforts have the greatest potential payoff in the larger counties, whereas smaller counties may have special needs for controlling crime in specific categories (i.e. burglaries in Wexford County). Tabular and graphic data illustrate the findings. Appendixes present data values and histograms, county populations, State offense and arrest data, and a matrix of difference scores for robbery.