The Buckeyes (7-1, 4-0, No. 16 CFP) won their sixth in a row -- five by lopsided scores. Now they head into the game of the year in the conference, at defending champion Michigan State next week.
Donovonn Young's 5-yard run late in the third quarter broke up the shutout for the Illini (4-5, 1-4). They have dropped four of their last five.
Barrett, nursing a sprained medial collateral ligament in his left knee and wearing a brace, left at halftime with the Buckeyes up 31-0. He completed 15 of 24 passes for 167 yards.
He gave way to Cardale Jones, who lofted a picture-perfect 27-yard TD pass to Dontre Wilson and also hit Michael Thomas on a 19-yard scoring pass. Jones was 5 of 9 for 82 yards passing.
After their first possession of the second half, Illinois quarterbacks Reilly O'Toole and Aaron Bailey had combined for 58 yards passing -- and 56 of them came on O'Toole's completion to Mike Dudek.
Dudek set the school mark for yards receiving by a freshman on the play.
Bailey, 9 of 16 for 79 yards without an interception, completed a 7-yard TD pass to tight end Matt LaCosse to close the scoring. O'Toole ended up 4 of 11 for 58 yards with two interceptions.
Samuel ran for 63 yards on nine carries and Ezekiel Elliott had 69 on nine for the Buckeyes, who have won the last six meetings.
The Buckeyes substituted heavily in the second half while a crowd of 106,961 left early as the score mounted. The game was played in windy conditions with temperatures in the mid-30s.
The 20th consecutive Big Ten regular-season win matched the mark set by Ohio State teams from 2005-07.
Unlike a week ago, when the Buckeyes rolled to a 17-0 halftime lead at Penn State only to struggle before pulling out a 31-24 victory in double overtime, this one was a landslide early.
The Buckeyes relied on the Illini's largesse in the opening half.
Illinois threw two interceptions -- both of which were off receivers' hands -- and also lost a fumble. The Buckeyes failed on two fourth-down runs deep in opposition territory, punted once -- and scored on the other five possessions.
O'Toole was intercepted by Darron Lee nine plays after the opening kickoff, with the Buckeyes taking just three plays to cover 38 yards. Samuel -- who got the start in place of leading rusher Elliott -- covered the final 23 yards untouched.
Barrett hit Smith on a 32-yard scoring toss to make it 17-0 before Samuel split two tacklers on a 1-yard plunge. Barrett found Smith on an 8-yard score for a 31-0 halftime lead.
The Illini were hurt by their own mistakes. Twice they were called for chop blocks to stifle drives and coach Tim Beckman, already on the hot seat after going just 10-23 in three seasons, was flagged for an unsportsmanlike conduct call for berating the officials.
The officials also had an off night. They whistled an Ohio State punt dead because the Illini had 12 men on the field, but then it was determined that the refs had miscounted. The Illini had the allotted 11. No flag.
An official also left his microphone on throughout the halftime show and it was easy to hear laughter and small talk as the band performed.
It was that kind of night.