Callahan is a small town located in the County of Nassau. This place is close to the downtown area of Jacksonville. Callahan has a total area of about 3.5 sq. kms. and is located at an elevated height of about 20 ft. from the ground level. With a large number of educational institutes in the area, the education system is the principal source of all major economic activities in the area. Most of the other industries have grown up based on the education industry.