Objectives: This study examines the relationships between indoor radon concentrations and distribution from soil geological mapping in the Hwacheon and Jangsu areas. Methods: GIS and a pivot table were used for inquiries about indoor radon contents, soil characteristics, and geological differences. Results: The Hwacheon area was characterized by the presence of normal and reverse faults as a passage of runoff for radon, sufficient occurrences of minerals containing uranium within granite as a radon source, a high concentration of radon within the granite area and clear differences of radon concentrations between granitic and metamorphic areas. The Jangsu area was characterized by the presence of normal faults, wide distributions of alluvium, and ambiguities on radon concentrations indoors among areas of geological differences. Considering the granite area and alluvium surrounded with granite areas, the characteristics of radon concentrations within soils and indoors in the Jangsu area are similar to those of the Hwacheon area. High concentrations are found with entisol and inceptisol in the Hawcheon area, but with entisol, inceptisol, and ultisol in the Jangsu area. High radon concentrations are found in sandy loam and/or loam. High concentrations are found in recently constructed or brick buildings, but low concentrations in traditional or prefabricated houses showing a high possibility of outward flow. Conclusions: The overall results suggest that radon concentrations in the Hwacheon and Jangsu area are dominantly influenced by geological characteristics with additional artificial influences.