Two men, both 41, were shot just before 2:20 p.m., one fatally, according to the Gary Police Department.
Several cars were left riddled with bullet holes in the parking lot outside St. Monica and Luke Church, in the 600-block of Rhode Island Street.
The victim killed was from Merrillville. The wounded victim is from Gary and stabilized, police said.
In a news release, the Diocese of Gary said family had received permission to rent the church's parish hall for a repast following a burial of a family member.
The diocese confirms the family who rented the hall were not parishioners.
"We pray for the family and their loved ones, may (they) be comforted as they begin to process this terrible tragedy," said Bishop Robert McClory.
Gary Mayor Jerome Prince offered his condolences, saying "It is beyond comprehension how anyone can attack a family already in mourning."
No one is in custody.