Is a sheriff, commonly called a county sheriff, elected by the voters of a single county, paid by a single county, and with jurisdiction over a single county nonetheless a state official? This seems like a simple enough question. Folks from the state attorney general's office are state officials, city employees are city officials, and county officials are, well, county officials. But in an effort to curtail Section 1983 lawsuits, five members of the Supreme Court in McMillian v. Monroe County (here), held that a county sheriff was a state official. It was an activist result, but it's nonetheless part of the law of Section 1983.
Whether a county sheriff in Georgia is a state or county official is again controversial in a lawsuit stemming from the Georgia courthouse shootings. A few months ago, because of lackluster security, a suspect killed a judge. The judge's widow is suing, arguing that but for the lax security, the judge would not have been murdered. The widow has sued, among others people, the county sheriff and the county. Since the widow's suit was brought under state law, McMillian is not binding authority.
If the county sheriff is a county official, then the county can be sued. If the county official acts for the state of Georgia, the county can't be sued, since the sheriff would be said to have acted for Georgia. Georgia, as all states are, is immune from suit.
This a major issue in the pending litigation, and Steven Pollack has an interesting summary of the legal issues in this article.