You can get an idea as to how concerned you should be about radon in your house by learning about the geology of the site and its radon potential. If your house is in an area the Environmental Protection Agency (EPA) shows has a high potential for radon, then chances are that your house may have an indoor radon problem. However, the way a house is built can increase the risk - so even in areas of low radon potential, some houses can have unhealthy radon levels.
USGS research on radon has mostly been limited to its presence in groundwater. The Environmental Protection Agency (EPA) is the best starting point for information about air quality and radon in buildings.