The key natural cause of irradiation in humans is the air. People spend most of their time at home, so home is likely a main source of natural radionuclide exposure in the air, especially radon gas. It is the second cause of lung cancer after smoking. This study aims to evaluate Radon‐222 gas (222Rn) concentrations in the houses (indoor dwellings) of the Al‐Hussainya district of the Karbala Governorate, Iraq. Also, some radiological parameters such as AED (annual effective dose), PAEC (potential alpha energy concentration), EP (exposure to radon progeny), and CPPP (lung cancer cases per year per million people) were calculated. 222Rn concentrations were determined using closed and open dosimeters with CN‐85 detector (thickness of 12 μm). The range and average of 222Rn concentrations were from 21.791 Bq/m3 to 43.376 Bq/m3 and 32.3381 Bq/m3 in open dosimeters, respectively. While in closed dosimeters, the range of 222Rn concentrations and average values were from 19.324 Bq/m3 to 37.286 Bq/m3 and 26.6462 Bq/m3, respectively. The average values of AED, PAEC, EP, and CPPP due to radon by open dosimeters were 0.083 mSv/y, 0.358 mWL, 14.759 mWLMY−1, and 1.503, respectively, while the average values of AED, PAEC, EP, and CPPP due to radon by closed dosimeters were 0.063 mSv/y, 0.270 mWL, 11.134 mWLMY−1, and 1.134, respectively. According to WHO, EPA, and ICRP, the values of radon concentrations were within the range of what was allowed internationally. Also, the results of the radiological parameters due to radon gas for the study of the houses of the Al‐Hussainya district of the Karbala Governorate, Iraq, were low and did not constitute a health hazard.