Goals from Kevin Thornton and Ben Tozer rendered Nile Cowperthwaite's late goal irrelevant as the Cobblers claimed all three points.
Johnson said: "We wanted to end the season on a high note and we did just that.
"We played pretty well and we were cheered on by more than 900 fans which was an absolutely magnificent following for us.
"They were here for a good day and I hope we helped make it one for them. We haven't won many games away from home and the fact we could have won this one by a lot more than we did says a lot about our side.
"On the face of it, it was a game with not a lot at stake but it was a chance for a few players to show me what they could do ahead of the summer and earn themselves contracts."
Source: PA
Source: PA