The topography is flat and the Chikugo River flows through the southeastern part of the town, forming the border with Kurume City.

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

During the Edo Period (1603-1867), Tachiarai was home to a community of Japanese hidden Christians (Kakure Kirishitans) who were present in the area since the 16th century, centered in the village of Imamura.

The community was quite successful in remaining hidden, avoiding being targeted by any crackdowns by the Tokugawa shogunate, which had banned Christianity on pain of death.

As with other Kakure Kirishitan communities, the so-called "Imamura Christians" had unique practices and beliefs, such as the cult of a saint-like figure called "Joan Mataemon" whose historicity remains uncertain.

This attracted attention from the local authorities as Christianity was still banned in Japan, resulting in a large number of arrests, although all were released by 1868.