This was a Milbank meter base/main service disconnect combo at the exterior. There was no main ground/GEC visible at the main panel and/or the exterior meter base. However, in the “chase” or compartment to the right there were 4 wires feeding up to the meter base. Now, does there need to be a “visible” GEC/ground wire here or can it be somewhere else where it’s not visible? TIA.
The GEC can land inside the meter box… do you have zoomed out pics of the enclosure? I cannot see this 4th wire in your pics, did you mean to say the left or the right that has the 4th wire?
On the right side you should have three wires running up to the meter. This is the primary service entrance. Appears to be a service lateral. The 4 wires are what is running to the interior main distribution panel. The ground and neutral are bonded at this point and should also have a wire running out to a ground rod. I do not see the grounding conductor to a ground rod and also the connection of the distribution feeder grounding conductor can not be split like this:
Do you have a better picture of the tag? Millbank has hundreds of meter breaker combo units to weed through to see if the location of the ground lug is in the meter compartment above the termination point pictured.
The far right side that’s covered had 4 wires running up to meter base, and then you can see factory wires supplying the main breaker.
No, I didn’t get one.
Wouldn’t there have to be a wire from that lug to the earth though, like a conventional set up? The only thing I can think of is that the ran the ground down the right side with the main wires had it connected below grade somewhere.
There was a green transformer box close by in the front yard if that makes a difference or not. Could the 4th wire be grounded out there or does it have to be at/on the house/structure?
Did you check for ground rods nearby 
Got pics of the box? perhaps that’s where the service point is.
No pic. You would need the ground/GEC at the building/structure though, no?
In this case, yes, it needs GEC landing between a service point and the terminals/neutral bus of the first disconnect.
I, however, do not know where the service point is in the installation you present in your pics. If it’s at the meter, then the GEC would land inside the meter box or the main disconnect. Since you have 4th conductor (as you claim – I cannot see it) on the right side going up to the meter, perhaps the rods are nearby and the GEC enters through the conduit going up to the meter enclosure from the ground. Otherwise, the service point could possibly be outside of the meter box.
Maybe @rmeier2 can help figure this one out