Wikipedia
A county attorney in many areas of the United States is the chief legal officer for a county or local judicial district. It is usually an elected position. The role of the county attorney can be similar to or complementary to that of a local state's attorney, commonwealth's attorney or district attorney.
In some jurisdictions, the county attorney oversees the operations of local prosecutors with respect to violations of county ordinances. In other jurisdictions, the county attorney prosecutes traffic matters and/or misdemeanors. In some states the county attorney prosecutes violations of state laws to the extent that the state permits local prosecution of these. County attorneys do not prosecute federal crimes, which are the jurisdiction of a United States Attorney.
Many county attorneys also bear responsibilities not related to criminal prosecution. These include defending the county against civil suits, occasionally initiating such suits on behalf of the county, preparing or reviewing contracts entered into by the county and providing legal advice and counsel to local government. In some jurisdictions, the county attorney does not handle any criminal matters at all, but serves only as the legal counsel to the county.
For example, in Arizona, Missouri, Montana, and Minnesota a county attorney represents the county and state within their county, prosecutes all felonies occurring within the county, and prosecutes misdemeanors occurring within unincorporated areas of the county. On the other hand, county attorneys in Kentucky and Virginia prosecute only certain misdemeanors and sometimes traffic matters and serve as legal counsel for their county, with felony prosecutions and prosecutions of offenses not handled by the county attorney being the responsibility of the commonwealth's attorney for the given county.