Kilmarnock took the lead in the seventh minute when Boyd's delivery across the face of goal fell to Johnston at the back post and he smashed the ball low into the far corner of the net.
Former Rangers striker Boyd popped up with the winner after Stuart Kettlewell had replied for the hosts, as Killie earned their first away win in the league this season.
"It's been brilliant to work with him day in day out in training - he wants the best from you and the goal he got was different class. It's great playing with a player like him," teenager Johnston said of Boyd.
"He helps you all the time throughout games, on and off the ball, especially to be in the right areas."
Johnston, capped by Scotland's Under-19s and highly regarded at Killie, also reserved special praise for manager Allan Johnston.
"The gaffer, he was a winger as well. He just tells me to get at them, one v one, just go take them on, that's brilliant I've got that freedom just to go and play," he said.
"He'll come up to you individually and give you tips on what to do. For instance, if the ball is on the other side get in the box at the back post, you don't know where it is going to break, and obviously I was in the right place when it broke for me today."
With both teams toiling towards the bottom of the table, the three points lifted Kilmarnock above County and into 10th place, and Johnston hopes they are now moving in the right direction.
"The most important thing was the three points," said Johnston, who was also on target in last week's 5-2 loss to Dundee United. "To come up here after a long journey and get the points is good - we go home happy.
"It was really massive win, we go above Ross County now but we need to kick on now.
"I feel confident, especially after getting a goal last week and getting one this week. It's brilliant for me and brilliant for the team."
- Sports & Recreation
- Stuart Kettlewell