The county was established on May 1, 1803, from Hamilton County; it is named for Dr. Joseph Warren, a hero of the Revolution who sent Paul Revere and the overlooked William Dawes on their famous rides and who died at the Battle of Bunker Hill.

[4] Warren County is part of the Cincinnati, OH-KY-IN Metropolitan Statistical Area.

: Beginning at the northeast corner of the county of Clermont, running thence west with the line of said county to the Little Miami; thence up the same with the meanders thereof to the north boundary of the first tier of sections in the second entire range of townships in the Miami Purchase; thence west to the northeast corner of Section No.

The Ohio Constitution requires that every county have an area of at least four hundred square miles (1,036 km2).

Clinton County's boundaries were several times adjusted in an effort to comply with that clause of the constitution.

One of them, the Act of January 30, 1815, detached a strip of land from the eastern side to give to Clinton.

The 1815 act was as follows: Except for the sections formed by the Great and Little Miamis, the sides are all straight lines.

[22] Warren County is home to the Mason Business Center, a 2-million-square-foot (0.19 km2) research and development facility for Procter and Gamble (P&G), whose global headquarters are located in downtown Cincinnati.

[23] Originally built in 1995 after three years of construction, P&G recently completed expansion of a new 500,000-square-foot (46,000 m2) Beauty and Innovation Center in 2019, adding an additional 1,000 jobs for a total of 2,800 employees at the site.

The original county commissioners in 1804 were Robert Benham, Matthias Corwin and William James.

Jimmy Carter is the only other Democrat since Franklin D. Roosevelt to win as much as 40 percent of the county's vote.

In local races, Warren County occasionally elected Democrats for much of the 20th century.

School districts include:[29] Non-geographic districts include: Warren County has no native colleges or universities, but was the original site selected for Miami University which instead located in Oxford, Ohio in 1809.

The University of Cincinnati owns 398 acres (1.61 km2) of land[30] at the intersections of I-71 and Wilmington road, but no plans for development on the site have been announced.

Navigation and communications equipment includes PAPI, AWOS, Pilot Controlled Lighting, and UNICOM.

Freight trains still serve Carlisle, and on a limited basis, Monroe, Mason, and Lebanon.

There have been proposals to run commuter trains from Cincinnati to the Kings Island area, but none have ever found sufficient support or funding.

[32] There is no public bus transportation based in Warren County, but there is limited service from Cincinnati to Mason and Kings Island.

Recreationally, the Little Miami River can be traveled by canoe or kayak for its length through the county, and motorized boating can be done at Caesar's Creek Lake.

The Star, like the Pulse-Journal in Mason and the Star-Press in Springboro, was owned by the parent of the Middletown Journal and the Dayton Daily News, Cox Media Group.

For a time in the mid-1990s, Lebanon was the home of commercial radio station WMMA-FM, begun by Mike and Marilyn McMurray in 1994.

It went off the air around 2010, and in 2012, the FCC removed WLMH from their database and cancelled their license as a result of no broadcasts for over a year.