At about the same time Illinois Governor Pat Quinn signed a gay marriage bill into law on Wednesday, Bishop Thomas John Paprocki of Springfield offered prayers of exorcism against the legislation.

With Quinn's signature, Illinois became the 16th state to allow gay couples to marry. The District of Columbia also approved a law in 2009.

(Related: IL Gov. Pat Quinn signs gay marriage bill.)

The head of the Springfield Roman Catholic Diocese held the service at the Cathedral of the Immaculate Conception.

“I exorcize you; every unclean spirit; every power of darkness; every incursion of the infernal enemy; every diabolical legion, cohort, and faction; in the name and power of our Lord Jesus Christ,” Paprocki said during the hourlong ceremony which attracted a large crowd of worshipers.

“Dare no more, O cunning serpent; to deceive the human race; to persecute the Church of God; to shake the chosen of God and sift them like wheat,” he continued.

In comments to The Chicago Tribune, Paprocki, a vocal opponent of the law, called the exorcism performed a minor one.

“I am not saying that anyone involved in the redefinition of marriage is possessed by the devil, which, if that were the case, would require the remedy of a major exorcism, but all of us are certainly subject to the devil's evil influences and in need of protection and deliverance from evil,” Paprocki said.

Paprocki told congregants that his prayers “are not meant to demonize anyone, but are intended to call attention to the diabolical influences of the devil that have penetrated our culture, both in the state and in the church.”

Politicians “responsible for enacting civil same-sex marriage legislation are morally complicit as co-operators in facilitating this grave sin,” Paprocki said.

A small group of activists who protested outside the cathedral labeled the service a stunt.

“I think the bishop is looking for publicity,” Erin Meehan told ABC Newschannel 20.