The vast majority of law enforcement agencies here in Colorado require a person to be POST certified before applying with them. Very few agencies run their own academies, so one almost always needs to attend an academy on their own dime (or use their GI Bill like I and many others did). After successful completion of the academy, your certification is good for only one year now, I believe (it was three years when I graduated) in which if you don't obtain employment by that time, you will need to attend a refresher course to obtain certification again.

All agencies are hard and competitive agencies to obtain employment with, especially all those in the metro area. Once you start looking in more rural (e.g. low income, low pay) areas, then the pool of candidates drops dramatically.