Billy McKay netted his 24th goal of the season from the spot after Charlie Taylor fell in the box under Mihael Kovacevic's challenge.
Thistle held out to move back above County into third place in the SPL, but Adams was left fuming with the major decision that went against the visitors on the hour.
He said: "It's not a penalty. Mihael Kovacevic won the ball and it's another big decision that has gone against us.
"Twice in the Scottish Cup match earlier in the season Inverness scored two offside goals. If I was Inverness I wouldn't be happy with the manner of that win.
"They have won 2-1 and they are jumping around with guys flinging their arms in the air, which is great, but it's another major decision that's not gone our way."