Terence Rafferty, of Chestnut Grove in Newry, was a priest in St Peter's Parish in Lurgan when the four offences took place during a six month period in 2001.
Rafferty, who was 38 years old at the time, maintained the physical relationship he had with the 16-year-old was consensual.
He stepped aside from his responsibilities as a priest following the allegation, which was made against him in April 2011.
However at Craigavon Crown Court on Thursday, Justice Gemma Loughran told Rafferty because of the girl's age, his actions were forbidden by law.
Rafferty's lawyers argued that his mental state had been brittle and vulnerable because he had dealt with some harrowing and terrible things as part of the Troubles.
Justice Gemma Loughran said sexual offences against children were a deplorable crime all too prevalent in today's society.
She said other priests had faced problems in their ministry without engaging in inappropriate sexual activity.
In delivering the sentence, the judge said she must follow the guidelines of the Courts of Appeal and sentenced Rafferty to a three year probation order.
He was also required to complete 100 hours of community service and spend five years on the Sex Offenders Register.
Rafferty has been disqualified from working with children and vulnerable adults for a period of 10 years.
Monsignor Hamill from the Dromore Diocese said there will be an internal church investigation into his crimes and Fr Rafferty will remain out of ministry "pending the outcome of that process".
"A betrayal of sacred trust occurred in this case and, on behalf of the diocese, I want to offer my sincere apologies for the anguish and distress which the complainant and her family have suffered and to give the reassurance that the safeguarding of children and young people is paramount," he added.
But campaigners said the sentence handed down to Terence Rafferty was the "latest in a long line of cases of clerical abuse where victims have been let down by the authorities".
Margaret McGuckin, Survivors and Victims of Institutional Abuse spokesperson, who was also in court with other victims, said: "Every month it seems there is another court case involving clerical abuse.
"Priests have had extraordinary access to children and young people through their roles in parishes, schools and youth clubs.
"There is a clear pattern over many years of clerics abusing the trust which families have placed in them by virtue of their powerful role within the community and of their crimes being covered up for many years, so endangering other children."