The Diocese of Joliet is facing another lawsuit claiming a now-deceased Catholic priest from a west suburban parish sexually abused three boys more than 30 years ago.

The three alleged victims were between 6 and 11 years old when they were abused by the Rev. Leonardo Mateo starting in about 1980, according to the suit filed Thursday in Cook County Circuit Court.

Mateo never faced criminal charges, and he died in 2004. The Joliet Diocese deemed allegations of abuse against him credible, according to diocese documents released in April.

The boys — two of whom are brothers — and their parents were parishioners at Immaculate Conception Parish, 134 Arthur St. in Elmhurst, when Mateo started inviting the children out for ice cream and fast food, the suit said. He also would take the boys to swim at the YMCA in Elmhurst, where he allegedly molested them in the pool or locker room.

Toward the end of the summer in 1982, a sister of the brothers witnessed Mateo abusing the boys at the YMCA and told her mother about it, the suit claims. Their parents went to Elmhurst police but didn’t press charges, instead demanding that Mateo leave the parish, the suits said.

The suit claims a diocese official came to the brothers’ homes to question them about the abuse and “trivialized” the claims, telling the boys that “if Father Mateo ever did it again, just tell him to grow up,” the suit said.

Soon after, Mateo was reassigned to a parish in Glen Ellyn, the suit said.

Before he was assigned to the Joliet Diocese in 1977, Mateo had been accused of sexual misconduct multiple times since he was ordained in the Philippines in 1959 and again when he worked in the Los Angelese Archdiocese — allegations that the diocese was aware of, according to the suit. He returned to the Philippines before he died in 2004, the suit says.

The plaintiffs claim the diocese hid “the true nature and scope of this problem of predatory and pedophile priests” to protect priests from criminal prosecution.

The Joliet Diocese was hit with five other abuse lawsuits in April against four priests including Mateo.

Cited in those suits in addition to Mateo were the Rev. Lee Ryan, who was removed from ministry in 2010, temporarily returned in 2012 and then removed again that year; the Rev. Lowell Fischer, who was removed from ministry in 2002 and is deceased; and the Rev. Frederick Lenczycki, who was removed from ministry in 2002, convicted of sexual abuse in 2004 and given a five-year prison sentence.

A representative for the Joliet Diocese could not immediately be reached for comment Thursday.

The 21-count suit seeks more than $1 million in damages.