In one office, about 10 years ago, we were not allowed to lock the door to our area even after the receptionist's estranged husband told our boss he was coming to the office to kill her, and anyone who got in his way. He had already broken the jaw of another male employee he saw talking to his wife. Needless to say, we were very nervous for the 3 weeks it took for the cops to find him.
When TN, sc, and I worked together, our offices were in a former hospital so they opened directly off the main corridor; not even a receptionist to see who was coming and going, citizens could walk right into our offices with no notice.
This was all at one county (which I left just last year), and I don't think they've ever had any kind of security plan, except stationing a useless rent-a-cop by the main entrance.