I am installing a dimmer switch in a few of my bedrooms and when I unscrewed the old switch there were three black wires, all three of them attached to the switch. My question is, is one of the black wires the ground wire. One is separate from the other two. Can anyone help if you understand what I am saying.

Thanks

Is there a 3 way switch in this circuit, another switch that also controls the light? Sounds like a 3 way. Is one black connected to the green screw? Can't imagine a black ground wire, code violation unless tagged for a ground.

Is your light only controlled by that one switch or can you operate it on another switch
Somewhere else in the room/house ? (2 switches can turn on and off the light alternatly)
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Usually light switches don't have ground wire (unless their body is metal (old switches) )
In that case you could see clearly one of the wires connected to that metal frame

All three black wires were attached to the old light switch. There is only one switch controlling and none of the lights are connected to any green screw. One of the black wires was connected to the screw on the light switch. I am ignorant when it comes to this.

The light is only controlled by the one switch. Should I connect the green wire to the one black wire that is under the other two?

If the wire was connected to a screw there is the possibility it is ground
Is there any way you can test for continuity to another known ground point (like an outlet socket with ground) ?
Do you have a multimiter or ohmimeter to ?

No I don't have any way of testing it

One is separate from the other two. Can anyone help if you understand what I am saying.

Are you saying that one wire was connected to one screw, another wire was connected to the other screw and the third was connect to a hole in the back of the switch?

One black wire was connected to the screw and the other two wires were connected through two holes in the back of the switch.

All new switches have a ground screw on the frame. That's because there is no ground on a plastic box. Do not connect a black wire to a ground wire or screw. By "holes in the back" we will assume push in connections. Are there white wires in the box? Sounds like you have 1 hot wire in and 2 switched power leads out. Maybe one of them controls an outlet. So, you will need to determine what is what and without a basic working knowledge and tools to help you, you will need some outside assistance since we cannot determine how your system was wired. It may only be 120VAC but under the right circumstances can seriously injure or kill you.

Can you post a photo of the wiring spliced as it was found?

You should have 3 white wires in the box connected together with a wire nut. You should also have an outlet or another light that does not work. You need to find that outlet or light. The outlet may be in the same room or it may be in another room.

Mark the 3 black wires A,B and C.

After you have found the non working outlet/ light, connect wires A and B together with a wire nut. If the outlet/light works you have found the hot wires. If the outlet/light does not work, connect wires A and C. If the outlet/light does not work connect wires B and C.
In other words connect 2 wires together until the outlet/light works. Then cut a short piece of black wire about 6" long and connect it to the two black wires.

Then connect the short piece of wire and the third black wire to the dimmer switch. It does not matter which wire gets connected to which screw of the dimmer switch.

If there are bare wires in the switch box, all connected together, those are your ground wires. If you have ground wires connect them to the green screw of the dimmer switch with a short piece of bare wire. If you do not have ground wires do not connect anything to the green screw.