Located in far southeastern Saitama Prefecture at an elevation of only three meters above sea level, Yashio is on the central reaches of the Naka River, and is approximately 20 kilometers from downtown Tokyo.

Yashio has a humid subtropical climate (Köppen Cfa) characterized by warm summers and cool winters with light to no snowfall.

After the Meiji restoration, the area was transferred to the new Saitama Prefecture in 1871 and divided into villages with the creation of the modern municipalities system in 1889.

The Saitama Prefectural government has called on the 12 municipalities that use this sewer pipe to limit their sewage use, affecting a total of approximately 1.2 million people in the 12 cities and towns.

In terms of national politics, the city is part of Saitama 14th district of the lower house of the Diet of Japan.