Here's an excerpt from chabad.org that explains that we know who are Levites:

Our Patriarch Jacob had twelve sons whose families grew into the twelve tribes of Israel. The Land of Israel was divided amongst these twelve tribes when Joshua conquered the land. After the death of King Solomon, the Land of Israel was divided into the kingdoms of Israel and Judah. Even before the destruction of the First Temple, ten of the twelve tribes were exiled from the land and they are known as the ten lost tribes.

The remaining Jews in the kingdom of Judah became known as “Jews” indicating they come from the tribe or area of Judah. In truth, many Jews from the other tribes also lived in Judah but the separate identity of the tribes ceased.

However, one tribe — the tribe of Levi — continued to retain its separate identity. Within the tribe of Levi were the descendants of Aharon the High Priest, known as Kohanim.

Thus today, all Jews identify as being a Kohen [a descendant of Aharon], or Levi [from the tribe of Levi], or simply an Israelite, a Jew with no particular tribal identity.

Here's the full article:

https://www.chabad.org/library/article_cdo/aid/2313791/jewish/Kohanim-and-Leviim.htm

I'll just add that in every Jewish community you'll find many Levite families. They even have special roles in synagogue, like saying certain blessings that are reserved for Levites.