The bombs started arriving in Western US in late 1944 and at first no one really knew what they were. However, geologists sampled the sand and determined that it had come from a small section of beach east of Tokyo. Until the end of the war, the US Government asked media outlets not to report on the bombs in order to prevent the Japanese from tracking whether they were successful. This apparently worked because the Japanese pulled the funding for the bombs after only a few months of launches, assuming that the balloons weren't hitting their targets.
Overall, the bombs were not successful; less than 300 out of an estimated 9,000 have ever been found – around 3%. However, one bomb detonated in rural Oregon in spring 1945 and killed a pregnant woman and five children, making them the only American civilians killed in the US as a result of enemy action.
After the war, talk of the bombs began to spread and it was found that seven landed in Nebraska including one in Omaha, one landed ten miles from Detroit and another landed near Grand Rapids. Balloon bombs, while largely unsuccessful, continued to be discovered throughout the US and Canada following the war and one was even discovered in British Columbia in October 2014.