There are plenty of US cities' crime rates statistics online. You can go and check out this website: http://www.neighborhoodscout.com/md/college-park/crime/. I just checked out College ParK (where UMD is located) and Baltimore. It seems to me that College Park is quite safe. Baltimore is the major contributor for the crime rates in the state of Maryland. Check it out. You can also find the stats for other cities.
No doubt, things happened in big city. Unless you r going to a peaceful small town or a country area. So, no worry lo, just be careful and everything will be okay.