Ninety-nine of them to be exact.
It is estimated variously that many thousands of people actually died over the long term from these tests. These people are called the "down-winders." The only reason for having the tests was to generalize the experience to all humanity, to see if everyone could, in theory be killed by nuclear weapons. The hypothesis has been more or less confirmed.
Other underground nuclear tests released significant amounts of radioactive materials to the environment, millions of curies of it in fact. Many of the released isotopes have no decayed and are no longer radioactive. For instance, all of the iodine-131 is gone, as is all of the cesium-136 and cerium-144. These were the most radioactive substances, and many found their way completely around the world. However there are still significant quantities of other isotopes, including the actinides like plutonium, and fission products like strontium-90 and cesium-137.
If you would like to learn more about nuclear weapons testing, and happen to be in Nevada and are not interested in gambling or seeing Wayne Newton or Elvis impersonators, there is a curious, maybe even weird, museum you can visit: The Atomic Testing Museum.
http://www.ntshf.org/I have never been there, but according to the website pictures you can see wonderful mock ups of nuclear weapons.
My personal opinion is that all nuclear weapons in the world should be dismantled as quickly as is possible and the materials in them fissioned in nuclear reactors.