That depends on what country, and if USA, what state, and what timeframe. There are death certificates that may be available (although each state regulates who can acquire them). There are death registers and death indexes. If the person left a will or had a large estate probate records may give the date, and that may be the only record several centuries ago. If the person was in the military at the time of death, military records may provide that information. You need to be more specific.