The 23-year-old Blackwood, who made three fifties in his first five tests, played with a discipline and maturity that belied his inexperience to anchor the hosts' reply to England's first-innings total of 399.
James Tredwell was the pick of the England bowlers with test-best figures of four for 47 and James Anderson claimed two wickets to move within one of Ian Botham's England record of 383 victims.
Having played mainly conservatively Blackwood began to loosen up after passing his previous best score of 66 not out wand struck several boundaries including a towering six, his second of the innings.
He brought up his hundred with a single but two balls later Tredwell dismissed Jason Holder for 16, caught by Gary Ballance in the covers.
Kemar Roach was the next man to go when he feathered a nick through to wicketkeeper Jos Buttler - his fifth catch of the innings.
Jerome Taylor was carelessly run out for a duck after good work from Stuart Broad before Sulieman Benn (2) flicked an Anderson delivery straight to Joe Root at short leg.
The hosts had begun the day trailing by 244 and lost veteran Shivnarine Chanderpaul - who passed Mahela Jayawardene's total of 11,814 test runs to climb to seventh on the all-time list - for 46 when his tentative drive at Tredwell was pouched by Ben Stokes.
Blackwood, reprieved on Tuesday when he was caught in the slips off a no ball, had some fortune again when he edged another Stokes delivery when on 43 but Tredwell dropped a sharp catch in the gully.
England took the new ball but Blackwood and Danesh Ramdin survived aggressive bowling until Ramdin, on nine, edged a short delivery from Stuart Broad down the leg side through to Buttler.
Original source: Blackwood ton too little for Windies