The NFL’s tackle statistics only go back to 2001. Even Pro Football Reference’s tackle numbers go as far back as 1987, and those numbers are thoroughly incomplete. With all of those caveats out of the way, and please bear that in mind, as best as I can tell without access to other data, Pittsburgh Steelers safety Minkah Fitzpatrick has recorded more tackles this season than any other defensive back in franchise history—so far as we can tell.
The Steelers have had 39 individual seasons since 1987, based on Pro Football Reference’s data, in which any player has recorded at least 100 tackles.