County were dealt a blow when Tes Bramble failed a late fitness test on his injured groin; Anthony Pilkington was moved inside to partner Liam Dickinson in attack.
There was better news for Jim Gannon, though, when Rob Clare and Jason Taylor declared themselves fit.
Clare replaced James Tunnicliffe with Taylor coming in for Keith Briggs who unfortunately broke his ankle in the Boxing Day victory over Notts County.
Adam Griffin, who replaced Briggs on Tuesday, also started.
Grimsby started the game brightly but it was County who took the lead against the run of play.
With just seven minutes on the clock Michael Rose swung in a corner from the right which Mariners' keeper Phil Barnes punched into his own net.
Two minutes later Tony Dinning almost scored a fabulous goal when he spot Barnes off his line but hit his 40-yard free kick was just off target.
The Hatters were now well on top and Dinning came close again on 10 minutes with a right-foot shot that went wide.
County doubled their lead on 25 minutes when Stephen Gleeson fed Anthony Pilkington. The former Atherton striker was then denied a goalscoring opportunity when Nick Fenton handled the ball.
Fenton was red-carded but Dickinson failed to punish them further when his penalty hit the foot of the post.
It didn't take Dick long to redeem himself, though. Just three minutes later he volleyed Pilkington's cross home at the near post after more good work from the impressive Gleeson.
It was almost 3-0 on 34 minutes when Pilkington shot wide after the chance had been created by Dickinson and Gleeson.
Just before the break Taylor played a one-two with Taylor who saw his low shot spilled by Barnes who just managed to gather the ball just ahead of Pilkington.
Half-time: County 2 Grimsby Town 0
Grimsby pressed at the start of the second half but County soon got back on the front foot.
Pilkington came close on 51 minutes when Barnes pulled off a decent save from his far-post volley following a fine diagonal pass from Rose.
Two minutes later Taylor burst from midfield and curled a shot inches wide of the far post.
Clare was next to test the Mariners defence when he collected Dickinson's chest down and watched in dismay as his shot bounced clear off the post.
The outstanding Gareth Owen then came close with a header from Gleeson's corner.
Griffin saw a shot well saved as the Hatters continued to carve open the Mariners' defence.
The third goal finally arrived 12 minutes from time when substitute Michael Malcolm drilled the ball past Barnes from the edge of the box.
The former Spurs youngster almost grabbed a second two minutes later with a diving header from Rose's cross that Barnes did well to keep out.
The 'keeper then made an even better save to turn Clare's left-foot dive around the post.
A perfect day was tarnished, though, when man-of-the-match Taylor limped out of the action in stoppage time with what looked like a recurrence of he ankle injury that kept him out of the Boxing Day victory.
Red Cards
Fenton 25.
Yellow Cards
Rankin 45, Boshell 87
