Can I adopt a child if I'm single?

Well I'm not ready now but I really want to start a family when I get out of college. My best friend is a state trooper and he took a kid in and raised him...but never adopted...I was wanting to know if after college if I cant find a wife would i be alout to adopt as a single parent? I know caring for a kid is a lot of work and costs a lot of money, but I really just want a child to call my own(not now) and unlike most parents nowadays I will give him everything he wants