County-level law enforcement is essential, even in places where the agency handles few actual enforcement duties. In those cases, the county handles functions that free up local and state agents to focus exclusively on enforcing criminal and motor vehicle laws. There is an important distinction between local police forces in the United States and those of other countries. The founders of this country feared, with good reason, a strong central government that controlled every aspect of their lives. The result was the purposeful exclusion of a central police agency from the U.S. Constitution, in order to keep remote rulers from controlling everyone's lives.

The local level of law enforcement can be extremely broad-based and diverse depending upon the locale. Small rural departments will not offer the diversity and depth of a large city department, but often the smaller departments offer police officers an opportunity to handle a wide range of investigations that would normally be handled by specialists.

Although it's unlikely that the small-town patrol officer would head up an actual homicide investigation, even a rookie police officer can be expected to handle a major traffic accident investigation and, by virtue of being first on the scene, become the expert for that accident. In cases where death or serious bodily injury is the result of a traffic violation, the potential always exists for making a felony arrest based on an investigation. This kind of investigation is probably as close as many officers will come to handling the big cases. Larger departments routinely have traffic experts who deal with major traffic accidents, handling the formal investigation and personally making any subsequent arrests as a result.