I've owned my first home for a few years now, but have never truly known where my main water shutoff valve was, mainly because I've never really known how to identify it. I've looked around my utility room where my furnace, hot water heater, etc are, but nothing matches what I recall from my parent's home when they shut off the water there. For reference, my home was built in 1985.
The area I've circled in red is what I believe to be the main shutoff valve, but wanted to confirm before I messed with anything (note: I do not have any need to do anything with this at this time, just something I'd like to know in the event of an emergency). There are many valves in my utility room with my washer, dryer, furnace, hot water heater, etc. But based off of the images I've found from Googling, this seems to match some of the examples I've seen.
Slight side note, I'm also slightly confused at what looks to be a ground wire going from the green circle in the above image to the blue circle in the above image. This seems unnecessary and / or abnormal, but I'm no handyman (if the original question doesn't already infer that :)). Here are some close ups:
Yes, that looks like your main shutoff valve. It's normally the first valve on your water supply from where it enters your house, and typically before the water meter. In my house there is another valve on the other side of the meter that makes it possible to swap out the meter without draining the house.
The copper wire is part of our house's grounding. It jumps around the meter and insures that there is an electrically secure path "through" the meter. Because of the union joints and that some meter bodies are not electrically conductive, it provides a secure path. Also when the meter is being replaced.
Yes it is your main shut off valve. I'm assuming this is in a basement, from the looks. You're good on that.
The best experiment to prove this out is to turn the handle clockwise until it stops. This usually takes about 10 turns.
The wire attached is a grounding conductor which more than likely goes inside your breaker box .