Samson’s judgeship did not mark the end of the period of the judges. Both the high priest Eli and the prophet Samuel are accorded the designation of judges
(for Eli, see 1 Samuel 4:18; for Samuel, 1 Samuel 7:15). The institution of the judgeship only came to an end with the rise of the monarchy. As in all things, Judges is organized thematically and not chronologically.
31 Then his brothers and all his family came down and took him and brought him up and buried him between Zorah and Eshtaol in the tomb of Manoah his father. He had judged Israel twenty years.