Warren is part of the Cincinnati–Middletown, OH-KY-IN Metropolitan Statistical Area.
As of the census of 2000, there were 158,383 people, 55,966 households, and 43,261 families residing in the county. The population density was 396 people per square mile (153/km²). There were 58,692 housing units at an average density of 147 per square mile (57/km²). The racial makeup of the county was 94.66% White, 2.73% Black or African American, 0.18% Native American, 1.26% Asian, 0.03% Pacific Islander, 0.31% from other races, and 0.84% from two or more races. Hispanic or Latino of any race were 1.03% of the population.
There were 55,966 households out of which 39.70% had children under the age of 18 living with them, 66.20% were married couples living together, 8.00% had a female householder with no husband present, and 22.70% were non-families. 18.90% of all households were made up of individuals and 6.40% had someone living alone who was 65 years of age or older. The average household size was 2.72 and the average family size was 3.12.
In the county the population was spread out with 27.70% under the age of 18, 7.10% from 18 to 24, 34.00% from 25 to 44, 21.80% from 45 to 64, and 9.40% who are 66 years of age or older. The median age is 35 years. For every 100 females there were 102.60 males. For every 100 females age 18 and over, there were 102.40 males.
The median income for a household in the county was $57,952, and the median income for a family was $64,692. Males had a median income of $47,027 versus $30,862 for females. The per capita income for the county was $25,517. About 3.00% of families and 4.20% of the population were below the poverty line, including 4.40% of those under age 18 and 4.70% of those age 65 or over.
Interstates 71 and 75 pass through the county as do U.S. Highway 22/Ohio 3 and U.S. Highway 42. Other major highways through the county are State Routes 28, 48, 63, 73, 122, 123, 132, 350, and 741. Interstate 71 crosses over the Little Miami River at the Jeremiah Morrow Bridge, the tallest bridge in Ohio.
Warren County has one public airport, designated as Lebanon-Warren County Airport (KI68/I68). The runway is a 4502' x 65'paved and lighted North-South runway (01/19), and parallel taxiway. Navigation and communications equipment includes PAPI, AWOS,Pilot Controlled Lighting, and Unicom. The airport runway, taxiway, and navigation equipment is owned by the County. The county leases a public terminal, but other facilities are privately owned and operated under contract by a Fixed base operator. The airport serves general and business aviation, but has no commercial airlines.
There are also two privately owned operating airports in the county; Waynesville airport, also known as Red Stewart Field (K40I/40I), and Caesar Creek Gliderport (2OH9), both with grass runways. Operations have ceased at two former private paved runway airports, Brownie's Lebanon Airport (19I), and Lebanon San Mar Gale (OH79).
Warren County does not currently have passenger train service except for a scenic train that runs between Lebanon and Mason. Freight trains still serve Carlisle, and on a limited basis, Monroe, Mason, and Lebanon. Historically, there have been several trains that ran through the county whose stops became cities and villages. These trains include the Cincinnati, Lebanon and Northern Railway, the Middletown and Cincinnati Railroad, and the Little Miami Railroad whose path is now replaced by the Little Miami Bike Trail. There have been proposals to run commuter trains from Cincinnati to the Kings Island area, but none have ever found sufficient support or funding.
There is no public bus transportation based in Warren County, but there is limited service from Cincinnati to Mason and Kings Island. Middletown also runs bus service to eastern portions of Middletown that are located in Warren County.
There are currently no commercially navigable waterways in Warren County, but the Warren County Canal did operate in the 19th century as a branch of the Miami and Erie Canal,bringing freight to Lebanon by Canal Boat. 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.