Monk, who was Blagojevich's law school roommate and chief of staff during his first term as governor, entered a plea that had been postponed for months while his lawyer and federal prosecutors negotiated the terms.
Monk will be sentenced after the Blago trial, which is set to begin in June.
According to the proceedings, Monk helped Blago seek a 100th contribution from an unnamed racetrack executive.
In return for the executive's assistance in garnering financial support from other racing associates, Blago would sign a bill favorable for his industry.
Also revealed were further details about Blago's alleged schemes, including an attempt "to make money and control Illinois government" that started even before Blago's first election in 2002.
As part of the plea deal, Monk said Blago told him, in the fall 0f 2008, about plans to build new roads and "didn't need legislative approval." Monk was to be the point of contact for engineering companies' campaign contributions.
Monk says Blago told him "if they don't step up f- 'em.".
Before becoming a lobbyist, Monk was chairman of Blago's campaign fund.