I assume by ground wires you mean green or bare wires connected together and to the green screw on the switch. How many neutral (white) and hot (black or red) are there?

You say that you installed the dimmer years ago. Do you remember how you wired it then?

Three bare ground wires to green ground screw on switch, two black-hot-wires to the two screws on the switch. There is one neutral-white wire-connected to another neutral wire behind the switch.
The dimmer was a simple install, two black wires and a ground wire connected by wire nuts.
I installed the new switch by using a ground wire nut.
The reason for the switch replacement is I’ve been installing LEDs throughout the house and the dimmer switch was causing the LEDs to strobe.
It works well now.
Still curious why three ground wires though.
Thanks.
Bill

Within the box, can you see which ground wire is associated with which cable? Normally, each cable (metallic or non-metallic) has one ground, one hot, and one black, so the three ground wires means that there must be three cables, so one more black and two white wires are not accounted for. Do you know where the extra ground wires come from? I assume one goes to the light and one comes from the breaker box. Usually the problem is too few ground wires, not to many!

(edit) I misspoke: Each cable should have one ground, one hot (black) and one neutral (white).

No, unfortunately I can’t.
Like you, I assume one ground wire comes from the box and one goes to the light. But the third ground wire is an enigma.
It is indeed puzzling!
Thank you.
Regards,
Bill