Trinity (15-0) now leads Kentucky with 24 state championships and has won 12 titles since 2001.
Blackburn completed 14 of 16 passes for 222 yards and three touchdowns while rushing for 110 yards and two more scores.
Lafayette, last season's 6A runner-up, also lost 45-7 to the Shamrocks in the regular season.
Quinten Brown caught a 51-yard TD pass from Walker Wood to cut Lafayette's deficit to 27-21 in the third quarter before Trinity ran away with 28 unanswered points.
Wood finished 13 of 17 for 181 yards for Lafayette (13-2), which fell to 0-4 in the state finals.
Jovan Smith added 100 rushing yards and two touchdowns for Trinity.
Rondale Moore's 71-yard touchdown reception from Blackburn in the fourth quarter capped Trinity's offensive showcase of 481 yards.
