The Abukuma River runs through the eastern part (forming the border between the former towns of Adachi and Tōwa), flowing from south to north.

Nihonmatsu has a humid subtropical climate (Köppen Cfa) characterized by mild summers and cold winters with heavy snowfall.

It developed as post station on the Ōshū Kaidō highway and as the castle town of Nihonmatsu Domain, a 100,700 koku han, which was ruled by the Niwa clan under the Tokugawa shogunate) in the Edo period.

Nihonmatsu annexed the neighboring villages of Shiozawa, Dakeshita, Sugita, Ishii and Ohdaira on January 1, 1955 and was elevated to city status on October 1, 1958.

In terms of national politics, the city is part of Fukushima 2nd district of the lower house of the Diet of Japan.