Ohio was the first state created from the Northwest Territory on February 19, 1803. Warren County was established by an act of the first General Assembly of the State of Ohio, passed March 24, 1803. It was one of the first twelve counties formed in the new State of Ohio from a portion of what had been Hamilton County. It was named for General Joseph Warren who was a physician and Major General during the American Revolution. He lost his life at the Battle of Bunker Hill.

In 1803 Ichabod Corwin built the first Warren County court house. It was a log structure known as the Black Horse Tavern. It was not only the courthouse and a tavern, but traveling merchants brought their woven materials, sugar, spices and whatever else that could be transported easily and set up shop at the Tavern. At that time it was located between Silver and Mulberry Streets on the east side of Broadway in Lebanon. The first regular term of court was held there in the fall of 1803 with Judge Francis Dunlavy presiding. This court session included indictments for assault, battery and "one or two for affray".

The first court house constructed as such was built in 1806 at the southeast corner of the public square on land donated by Ichabod Corwin, Silas Hurin and Ephriam Hathaway. The first County Commissioners, Matthias Corwin, William James and Robert Benham drew up plans for the building in 1805 and commissioned Samuel McCray to build it for the sum of $1450. This building served Warren County for the next 30 years. In 1835 that building was given to the city to be used as a Town Hall and was eventually destroyed by fire in 1874.

In 1835 on the east side of the block at the intersection of East and Silver Streets the second court house was built at a cost of $25,000. In 1998 this building was renovated and is used to house numerous county offices. The county office building on the opposite corner of the Silver Street block was built in 1968 and houses additional county offices.

The Justice Center on Justice Drive in Lebanon houses the Common Pleas Courts. Also on Justice Drive are the Warren County Jail, the Sheriff's Offices, Juvenile Treatment Center, and Juvenile/Probate Court. A 100.000+ square foot Warren County Administration Building began operation in the year 2001 on Justice Drive.