I know there is a way, but I cannot find it. How can I identify the number of entities around me in a given block radius?

Create an AABB and use the method for finding all entities within the AABB?

Thanks for the push in the right direction.  It took me a few minutes, but I figured it out. Now it will identify any EntityMob within 5 blocks (if my understanding of the +5 is correct)

 

For those who actually would like to see some code:

 

List e = player.worldObj.getEntitiesWithinAABB(EntityMob.class, AxisAlignedBB.getBoundingBox(player.posX, player.posY, player.posZ, (player.posX + 5),(player.posY + 5),(player.posZ + 5)));

if (e.size() > 0) {

        	for (int i = 0; i <= e.size() - 1; i++) {
        		EntityMob em = (EntityMob) e.get(i);
        		LogHelper.info(em.getEntityName());
        	}    	
        	
        }   

Ok. I have this working for client side detection, but how do I make it identify the entities on the serverside? the method returns 0 everytime.

You've almost got it right. Now you're setting up a AABB for only a part of the radius. This can be solved by doing this:

List<EntityMob> e = player.worldObj.getEntitiesWithinAABB(EntityMob.class, AxisAlignedBB.getBoundingBox(player.posX - 5, player.posY - 5, player.posZ - 5, player.posX + 5, player.posY + 5, player.posZ + 5));

Checking for e.size() > 0 is unnecessary, as the test of the for loop will be false at the start (0 <= 0 - 1) = false. But this is a small side note.

 

This code should work at the server side as well....

 

By the way, if you want to have a real max of 5 blocks, you can use Pythagoras' theorem to filter out entities that are outside your radius (you're now checking in a box around the player).