When you sue in federal court, you have to put in your complaint the basis for the court's authority to hear the case (known as subject matter jurisdiction) and you have to put in the complaint a set of facts that, if proven true, would give rise to a recognized legal claim. You have not said what exactly it is that county did that violated your federal civil rights (you cannot sue a state/local government in federal court for a violation of state or local law). Without knowing what it is that county did that you allege violated your civil rights, I cannot say if it would be necessary to name the policy maker. However, if you are alleging that a certain county policy violates your rights you certainly have to include facts that show that the county in fact had such a policy. Who the policy maker would be depends on what policy this is and how that county is organized, which of course I don't know as you did not specify the county or the policy at issue.
Suing in federal court is not easy for someone unfamiliar with the federal rules of civil procedure, federal rules of evidence, and federal law, all of which are important to a federal lawsuit. The rules can get complex, especially when suing a government entity. You ought to consider getting a lawyer experienced in civil litigation in federal court to make sure you get it right. Depending on exactly what your claim is, you may be allowed to get your attorney's fees included in the judgment if you win and/or you may get an attorney to handle it on a contingent fee basis (which means the fee is a percentage of what the attorney recovers for you).