In the present study, concentration of radon- thoron and their progeny levels inside the kasimpur thermal power plant, Ukhalana and Sunamai villages were measured using the twin chamber solid state nuclear track detector (SSNTD) based dosimeters using 12 m thick celluslose nitrate based pelliculable LR-115 type II detectors. Twin chamber dosimeter cups fitted with LR-115 type II films were placed at 10 places inside the Kasimpur thermal power plant, 10 places in the dwellings of ukhalana village and 8 places in the dwellings of sunamai village. Radon concentration inside Kasimpur Thermal Power Plant vary from 16  2.9 Bq m-3 to 61 5.6 Bq m-3 whereas thoron concentration varies from 6  0.7 Bq m-3 to 56  5.1 Bq m-3. Radon and thoron PAEC values are found to vary from 1.73 0.31 mWL to 6.59 0.61 mWL and 0.16  0.02 mWL to 1.51  0.4 mWL. The annual effective dose from radon, and thoron is found to vary from 0.05 mSv y-1 to 0.95 mSv y-1. The life time fatality risk factor was also estimated and it varies from 0.0110-4 to 0.24  10-4. Radon concentration in the dwellings of Ukhalana village is found to vary from 13  2.54 Bq m-3 to 42 4.66 Bq m-3 whereas thoron concentration varies from 11  1.27 Bqm-3 to 39  4.08 Bq m-3 . Radon and thoron PAEC values vary from 1.41 0 .27 mWL to 4.54 0 .5 mWL and 0.29 0 .03 mWL to 1.05  0.11 mWL. The annual effective dose from radon, and thoron is found to vary from 0.063 mSv y-1 to 0.183 mSv y-1. Estimated life time fatality risk factor varies from 0.1910-4 to 0.5510-4 . The inhalation dose is found to vary from 0.64 mSv y-1 to 1.57 mSv y-1. The Radon concentration in the dwellings of Sunamai village is found to vary from 14  2.67 Bq m-3 to 58 5.51 Bq m-3 whereas thoron concentrations varies from 3  0.27 Bq m-3 to 57  4.97 Bq m-3. Radon and thoron PAEC values vary from 1.51  0.29 mWL to 6.27  0.59 mWL and 0.08  0.007 mWL to 1.54  0.13 mWL. The annual effective dose from radon, and thoron is found to vary from 0.066 mSv y-1 to 0.229 mSv y-1. The life time fatality risk factor was also estimated and varies from 0.1910-4 to .69  10-4.These values are below the recommended action levels.