The Lilajan begins its journey north of Simaria in Chatra district on the Hazaribagh plateau, the western portion of which constitutes a broad watershed between the Damodar drainage on the south and the Lilajan (also called Niranjan) and Mohana rivers on the north. It flows through a deep and rocky channel until it reaches the neighbourhood of Jori. There the hills begin to recede and the stream flows sluggishly over a wide sandy bed. From this point to the Gaya border beyond Hunterganj the river is a sandy one dry in summer but disastrous during the rains. About 10 kilometres (6 mi) south of Gaya it unites with the Mohana River to form Falgu River.
As Bodh Gaya is on the shores of Lilajan (Niranjan) many legends are associated with this river concerning Buddha. It is said that Buddha bathed in the nearby Niranjan (now called Lilajan) River after attaining enlightenment.