The model rests on the awareness that State police agencies in both rural and urban areas rarely have more than one unit available to handle a call. In Illinois, as in other States, most of the State policing is traffic-related, and calls for service generally occur in rural areas. Individual patrols cover several hundred square miles and have limited support from other units, except in urban areas, where assistance comes from other departments rather than from other State police officers. The model focuses on providing visible preventive patrol together with adequate responses to calls for service. The model considers the frequency of calls for service, the area served, the desired response time, the average responding speed, and the desired level of preventive patrol. The model aids the computation of the number of police officers needed and easily handles changes based on new assumptions. Equations, tables, 17 references, and appended methodological information.