The vast majority of the cases began while migrants were detained, not beforehand.
Temple University in Philadelphia had been dealing with a similar outbreak that sickened more than 100 people.
Philadelphia's health department expects the outbreak to continue "for a while longer" and encourages vaccinating.
ICE detention centers throughout the country have quarantined migrants after outbreaks of mumps, influenza and chicken pox.
Health officials say there’s no evidence the disease was transmitted outside the facility.
You can get mumps even if you’re vaccinated, though your symptoms likely won’t be as bad.