As of March 2011, the city has an estimated population of 64,467 and a population density of 485 persons per km². The total area is 132.99 km².
The modern city of Sanyo-Onoda was established on March 22, 2005, from the merger of the city of Onoda, with the town of Sanyo (from Asa District).
Sanyo-Onoda is between Ube and Asa, and is largely an industrial town. It has a beach area called Kirara Beach, a manmade beach that has a few restaurants and a glass-making factory. There is a fireworks festival every July/August and a number of smaller festivals celebrating old people and primary school children and education.
The cherry blossom festival at Wakayama and Sue Parks are very popular with families and groups during the blossom season. Mount Ryūō provides a view of the area from Ube to Asa and across to Kyushu. There is an old Shinto shrine at the foot of Mount Ryuou called Akasaki shrine.
There are a number of restaurants in Sanyo-Onoda, anything from okonomiyaki to sashimi to izakaya, udon and generic fare. A bus system runs through the major roads and a local train line in addition to the main Sanyo line.
The weather is mild. It snows a little in winter and is humid in summer, but most of the high winds and heavy snowfall are avoided due to the proximity to the coast. It does, however, experience a strong typhoon season.