From January 1 to January 28, 2017, 27 states in the U.S. reported mumps infections in 495 people to CDC.
Mumps is no longer very common in the United States. From year to year, mumps cases can range from roughly a couple hundred to a couple thousand. For example in 2016, there were 5,311 cases reported to CDC, and in 2012, there were 229. Before the U.S. mumps vaccination program started in 1967, about 186,000 cases were reported each year, but the actual number of cases was likely much higher due to underreporting. Since the pre-vaccine era, there has been a more than 99% decrease in mumps cases in the United States.