I've been curious about this too. I have a sheet with all the 10 codes but I've heard them using 10-100's lately and my list stops at 10-99. Anyone know about the codes that are above 10-99 in Iowa. Marion county here.
In Dubuque, at least when I worked as a Reserve officer, the Code 1-2-3-4 were related to how long you had to respond to call. In our case code 1 was lights and siren, try to arrive as quickly as possible, safely. Code 2 was hurry, but no lights and siren (maybe lights to get through the stop lights) Code three was maybe within 1/2 hour to hour code 4 within 4 hours and code 5 by end of shift. It may have changed somewhat, but it is clear that locally code 1 stands for a emergency response yet. It might vary in other communities.