The Magpies did not look like a team bottom of the league as they more than matched their promotion-chasing opposition.
Brentford goalkeeper David Button was forced into action early on, making a double save to deny Grealish and Danny Haynes while Callum McGregor had an effort cleared off the line by Clayton Donaldson.
But the hosts fell behind in the 44th minute as the Bees netted with their first effort of the game.
Derry's men continued to press in the second half but Brentford should have sealed the game on the hour mark as Donaldson burst clear, only to scuff his effort wide of the post.
Donaldson missed another decent chance soon afterwards when he headed Jake Bidwell's free-kick past the post while Grigg fired straight at Bartosz Bialkowski late on.
McGregor might have snatched a point for County in injury time but Button parried his shot wide.
"I was delighted with the first half but a bit disappointed with the second because we could have done more," said Derry.
"When you concede that close to half-time, though, it changes the whole complexion of the game. We went from a team full of confidence and not wanting the half to stop, to a team with our heads down.
"We've got to take heart from what we have achieved.
"We have played another good team and even the most sceptical Notts County fan would say we deserved to get points out of this game and the last game here against Wolves."
- Sports & Recreation
- Clayton Donaldson
- David Button