While some information can be got from living relatives, probing earlier requires searching various records such as immigration files, church records, county databases and the like. This activity is greatly facilitated by the Mormans in Utah. Their religious beliefs emphasize very strongly that everyone and their ancestors should be baptized. This, as the first step, requires locating the ancestors. To this end they have amassed a huge depository of records of all sorts relating to births, deaths, etc.
Years ago one had to find a Morman church with copies of such data. Nowadays, computer access makes searching much more feasible.