In eukaryotic cells, it's stored in the nucleus. Mithochondria, however, contain some DNA, which is called mitochondrial DNA. So, then, most of the genetic material is within the nucleus.
In prokaryotic cells, it can be found free-floating in the cytoplasm. At least, that's the best way to explain it. It's not contained in a nucleus in prokaryotics cells.
In viruses, it can be found within a protective protein coat.