There are two distinct issues here.
First, you need a model release if you are photographing a recognizable individual. Traditionally, model releases were only required if you were using the image for commercial purposes, and not if your purpose was journalistic or artistic. However, the surfeit of lawyers in the US has led to the situation where it is becoming prudent to ask for model releases for non-commercial photographs of people. I also believe that it is generally unwise to photograph a nude model without asking for a model release. A signed model release simply means that the subject has consented to being photographed and to the potential uses of that photograph described in the model release.
Now, the issue of 'public places' is a totally separate matter. The owner of private property has the right to impose constraints on the practice of photography on his property - no matter what the subject is. So, for example, the owner of a shopping mall is perfectly within his legal rights to say that photography is not allowed in his mall - and it doesn't matter whether you want to photograph people, frogs, or salt shakers, you can't do it. The mall is private property, no matter that the public has free access. So the 'public place' issue is not how can you use the images, but rather can you photograph at all.
Photography is perfectly legal on public property. Sure, there have been the occasional news reports of police hassling photographers, but those are exceptions, not the rule. Obviously, if your photography causes acts to be committed that are illegal, you may have a problem. For example, photographing a nude model in a public place can get you in trouble - not because you are photographing, but rather because you have asked the model to be nude in a public place.
So you need to ask yourself:
1. What use do you have for your photographs? If you don't have a model release, you probably can't sell them for commercial use (eg, advertising), but unless you defame the subjects in some way, you probably can use them in artistic displays or even some journalistic setting. You might want to consider whether the images might convey an unwanted message about the subject, and avoid those images since they could result in legal problems - not because you don't have a model release, but rather because they defame the character of the subject. Where you made the photographs is generally not an issue. However, if the setting is recognizable, and if it is private property, then you may need a property release.
2. Is the college where you are currently photographing privately-owned, or is it a public institution? If it is a public institution, then there is no reason to stop making photographs. If it is privately owned, you may have an encounter with a rent-a-cop and he would be correct in asking you to stop photographing. However, he would not have the right to confiscate your camera, make you show him your images, or destroy your film (or erase you memory chip). And once you have the images, you need to go back to rule 1 to determine how you can use them.