As April 1, 2011, the city has an estimated population of 163,954, with 62,714 households, and a population density of 955.39 persons per km2. The total area is 171.61 km2.
In 2006, Oyama became the second most populous city in the Tochigi prefecture, with the capital of the prefecture Utsunomiya retaining the number one spot.
The city is centred around Omoigawa River.
Oyama was given city status on March 31, 1954.
The mayor of Oyama is Toshio Okubo.
One of the major employers in the city is Komatsu making iron castings, diesel engines, fork lift trucks and other hydraulic equipment.
Oyama formally signed a sister-city agreement with Lübz, Germany in 2003 and with Cairns, Australia on May 15, 2006.