Columbia is a very safe city with a crime rate well below the national average.  One can feel safe walking the streets at any time, day or night.  The campus and downtown area is very safe, even after the bars close at 1 p.m.  That said, just to be on the safe side,  avoid venturing north of Walnut Street after 10 p.m.  Walnut St. is located downtown, one block north of Broadway.