The primary cause of natural background radiation exposure in the general public has been radon and its shortlived decay products in homes, which account for around 50% of the population's effective dose worldwide. Radon (222Rn) and its progeny inside building and environments have been recognized as a global issue and a substantial risk factor for lung cancer. In this research,Inspector alert nuclear radiation meter (manufactured by S.E international U.S.A SN:35440) with inbuilt Geiger-Muller tube was employed to determine the concentration of 222Rn in the eleven (11) investigated points at Junior Secondary School Idu-Koro Abuja, to calculate the tenants' effective dose from 222Rn and its progeny. The meter was held at the abdominal level (about 1 m above the ground surface). The dosimetric measurements were taken in count per minute (cpm) mode and the radon concentration range from to . Conversion was made from count rate to dose rate, absorb dose rate, annual dose rate and finally effective dose rate for comparison. The effective dose to the occupants was estimated ranging from to , with a mean of . The radon contents were establish to be lesser than the reference value from the international commission for radiological protection (ICRP) as the appropriate safety; hence it may not result to any health effect of lung cancer to the occupants and the members of public within the investigated areas.