Ohio county government is the structure of official managerial and legal bodies of the counties of Ohio, USA. It is marked by a loose organization and a diffusion of power, the basic framework not having been changed since the nineteenth century. The Ohio Constitution allows counties to set up a home rule charter government as many cities and villages do, but only Summit and Cuyahoga counties have done so.

Counties operating under a constitutional government operate under Dillon's Rule. They are creatures of the state, and have only those powers granted to them by the Ohio General Assembly and the Ohio Constitution, any power implied by those express powers, and those powers essential to their existence. However, Article X of the Ohio Constitution gives county government benefits similar to those conferred on cities and villages under the home rule amendments of 1912.

Eighty-six of Ohio's 88 counties (all except Summit as of 1981 and Cuyahoga as of 2011) have the following elected officials as provided by statute:

All of these officials are elected to four-year terms in November of even-numbered years after being nominated in partisan primary elections. One commissioner and the auditor are elected in the same year as the governor in one cycle; the other two commissioners and the other officials are elected in the same year as the president of the United States. The clerk, coroner, engineer, prosecutor, recorder, and sheriff begin their terms on the first Monday in January. The auditor's term begins on the second Monday in March. The treasurer's term begins on the first Monday in September. The commissioner who is elected with the governor begins his term on January 1. Of the other two seats, one term begins on January 2 and the second on January 3.

Any citizen of Ohio and the United States who is 18 years of age or older and lives in the county may run for commissioner, auditor, treasurer, clerk of courts, or recorder. The other offices have specific additional requirements: candidates for prosecutor must be licensed to practice law; candidates for coroner must be licensed to practice medicine for two years; candidates for engineer must be both licensed surveyors and engineers; and candidates for sheriff must have either a two-year college degree or five years of supervisory experience in law enforcement.

If a vacancy arises, it is filled by the county central committee of the political party to which the former official belonged, i.e., the Republicans appoint someone to an office held by a Republican and the Democrats to an office held by a Democrat. If an office becomes vacant before the November election in the even-numbered year midway through the term, the appointee must run in a special election for the remainder of the term. If the office becomes vacant after then, the appointment is for the remainder of the term.

The Board of County Commissioners is the combined executive and legislative branch of county government but as their control over the independently elected officials is limited, there is effectively no real executive. Though the commissioners receive a full-time salary, most commissioners have full-time occupations on the side and so many boards hire a county administrator to oversee the county's day-to-day affairs. The board also employs a clerk to record its proceedings if it is deemed necessary to have a full-time clerk, otherwise the Auditor is ex officio the clerk. One of the members of the board is named president of the board.

The board of commissioners often create numerous subordinate departments to handle specific services. These vary from county to county; among the most common are departments for building and zoning, health, economic development, water and sewer service, and emergency management.