FBCHammond.com

Pastor Jack Schaap's profile has been removed from the web site of the First Baptist Church.

CHICAGO - The former pastor of an Indiana Baptist megachurch is being investigated for sexual relations with a teenage girl, and the church is cooperating with authorities probing whether any of the behavior was criminal, a church official said Thursday.

Jack Schaap, 54, pastor for 11 years at the First Baptist Church of Hammond, confessed to having sex with a member of the church when she was 16, said Eddie Wilson, director of public relations for the church.

The church, located in the Chicago metropolitan area, has 40,000 members and typically has 15,000 people in church on any given Sunday, Wilson said.

Adultery is grounds for dismissal under the church's bylaws, and Schaap was fired on Monday following an internal investigation, Wilson said. Schaap and his wife are trying to reconcile their marriage, he said.

The age of consent in Indiana is 16. FBI became involved because Schaap is accused of taking girl across state lines to Illinois -- where the consent age is 17 -- when she was 16, NBCChicago.com reported.

"It was starting to be a difficult decision, but when we found out the facts, we had no choice.  We had to do what was right," the NBC affiliate quoted Board of Deacons Chairman Jerry Duff as saying.

The deacon's board reported the information to Lake County Sheriff John Buncich first thing Tuesday morning, Wilson said. Buncich was not immediately available for comment.

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Schaap, who could not be reached for comment,  had been employed by the church and associated Hyles-Anderson College for about 30 years, Wilson said. Wilson said the ex-pastor was "in seclusion" with his wife, Wilson told Reuters. 

Schaap's wife is the daughter of Jack Hyles, the pastor who built the church, NBCChicago reported.

Trisha Kee, who said she is a victim advocate for people abused at Independent Fundamental Baptist churches and had attended Hyles-Anderson College, told Reuters that Schaap's behavior was discovered accidentally at a youth conference last week.

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She said Schaap left his phone on the pulpit. A deacon found it, and a text came through from the girl that revealed the relationship, said Kee, who runs a Facebook group for ex-congregants. 

One parishioner told NBCChicago that while he was heartbroken he would not hold a grudge against his leader.

"I know God put him in that position for a reason and what he did is a mistake, and God will forgive him," parishioner Jesus Perez said.

Reuters and NBC News staff contributed to this report.

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