Mason is a city in southwestern Warren County, Ohio, United States, approximately 22 miles (35 km) from downtown Cincinnati. As of the 2010 census, Mason's population was 30,712.
Mason is home to Kings Island amusement park and one of the largest tennis stadiums in the world, the Lindner Family Tennis Center, home of the Western & Southern Open, one of the world's top tennis tournaments for both men and women.
On June 1, 1803, Revolutionary War veteran William Mason paid $1,700 at auction to purchase 640 acres (2.6 km2) of land in what is now downtown Mason. In 1815, he platted 16 lots on this land and named the village "Narnia" In 1832, two years after the death of William Mason and according to his will, more than 40 additional lots were platted on the north, south, and west of Narnia. When the plat was officially recorded, the name of the village was listed as "Palmyra."
In 1835, a petition was sent to the federal post office to correct the name of the town. It had been listed as Kirkwood, possibly an error because the postmaster at the time was William Kirkwood. When village officials were informed that there was another Palmyra in Ohio, the name was officially changed to "Mason."
Mason remained a small farming community for another 125 years. In 1970, a year before the town was incorporated to become a city, there were fewer than 5,700 residents.
In February 1997, Mason withdrew from surrounding Deerfield Township by forming a paper township called Mason Township.
The median income for a household in the city was $89,569, and the median income for a family was $103,459. Males had a median income of $96,002 and females had a median income of $75,968. The per capita income for the city was $37,948.