"That helps keep the possibility down if they've been exposed," Carney told IndyStar. "We had about 58 percent of the frat that took part of it."
The new count more than doubles the seven cases reported last week, according to WXIN Fox 59.
University officials say the first two students confirmed with the mumps were roommates who lived off campus. The third student diagnosed with mumps received the measles, mumps and rubella vaccination, which is required for students to attend school.
This year, Indiana is one of the 10 most infected states in the country.
Anyone who has come in contact with the infected students can get a free vaccine, the university said.
People who contract the mumps are contagious from two days before showing symptoms until five days after symptoms start.
The mumps was almost non-existent in the United States after the two-dose vaccination program, introduced in 1989, wiped out 99 percent of the country's cases. Then in 2006, the country began seeing outbreaks of mumps every five years.
The Centers for Disease Control and Prevention calls three or more cases of mumps an outbreak.
Symptoms of the mumps include swollen glands, headache, loss of appetite, muscle aches and fever, which for most people subside after two weeks.
The CDC says keeping good hygiene and getting the MMR vaccine are the best way to protect against the mumps.