Lennon felt the performance was one of the worst that he had witnessed since taking charge in June 2010.
"I'm proud of my players prior to the game, they've got a focus to go and show the nation live on Sky what we're all about at this football club and we were very much a shadow of ourselves," Lennon said.
"I do believe in this group of players and we certainly had a bad day at the office.
"The key thing to our success over recent months has been our endeavour, our commitment, our belief and more importantly the work-rate, which has been absolutely incredible until yesterday.
"There was a lack of passion, a lack of desire, a lack of fight and it really hurts me."
Debutant Ivan Sproule netted a double as the Highland side turned in an impressive display.
Richard Brittain fired the visitors ahead with an excellent 25-yard free-kick after 22 minutes and Adams' side passed up numerous opportunities to extend their advantage during the first half.
St Mirren levelled five minutes into the second half before Sam Morrow took advantage of a defensive howler by David Barron to restore County's lead.
Sproule added a third four minutes later and then capped off an excellent performance when he tapped home a fourth.