We did not snowshoe the Cooper River. We walked the Salmon la Sac campground loop and the Cooper River runs right by here, so it was the closest thing in the WTA library. This makes a great walk this time of year. It is groomed and quiet on a weekday. I should have brought snowshoes because we occasionally, like 50 times, broke through a few inches or a little more, which is very irritating. We saw two other people on the loop who were smarter that we were because they had snowshoes. The rivers here pretty much surround the campground, so we were in sight and sound of water the whole time. This winter has had both ridiculous snowfall and a ridiculously long sunny dry spell around here. Today was brilliantly sunny and warm for February, and we’ve had a lot of that. For this loop you park a quarter mile or so before the campground on the road where the signs tell you to. A Snopark is needed, unless you are lucky and don’t get checked. The loop takes and hour or so, and is quite enjoyable. 

We arrived at the trailhead by 9 am on New Year's Eve Day. The road has been plowed and is packed-snow-covered but did not feel icy; my AWD HR-V handled the conditions with aplomb without chains. The trail was broken for us by previous snowshoers. We went just under three miles in and then turned around to return to the trailhead at noon. The trail goes through beautiful snow-covered forest with just a few peaks at the river below. We encountered a few snowmobiles on the road to the trail but there were none once you go into the woods. It was very quiet and we met under ten other people on the trail. 

As others have noted, you have to go down to the trailhead itself (there are several small buildings and the privy was open), turn around, and park along the road facing the direction that you came. The signs marking the limits of the parking areas were covered in plow-flung snow but we were given directions by a kind snowmobiler to make sure that we didn't get a ticket. Sno-park pass required. 

We left Seattle at 6:30 am and returned by 3:30 pm. My friend introduced me to Stella's in Cle Elum, where we got a delicious lunch and I treated myself to a chai. YUM.

Very beautiful & quiet snowshoe. We had very limited time and barely went a mile on the trail itself before stopping for lunch and turning around but I highly recommend it and plan to come back to do the whole route.

Directions - Put Salmon La Sac Campground as destination in google maps although you will have to turn around at the end and go back down Salmon La Sac Rd / 903 to find the closest parking spot, which is sno-park permit only parallel park style alternating right / left in sections approaching the end of the road. We found a spot between the numerous trucks pulling snowmobile trailers in the section closest to the end of the plowed road, which is not far from the historic depot lot, around 10:30. To reach the Cooper River TH, you must walk up Salmon La Sac Rd across the bridge towards and past the Salmon La Sac campground, until you come across a little outhouse and board / signage for the trailhead. It is listed 'Salmon La Sac Trailhead' on google maps but we used the Hiking Project app to find the Cooper River TH.

We were the only ones on the trail today and didn't hear any snowmobiles although there were plenty when we parked. They were heading up NF-4330 when we turned left to cross the bridge and continue on Salmon La Sac Rd on the road walk.

Lots of snow on the trail, we broke it in more from a faint-ish outline but only for a short ways. General orientation with the river on the left and obviously not walking off the steep edges / cliffs will keep you on the right track. As others mention, you don't see more than glimpses of the river except at the start, but the woods are stunning in themselves.

Went to the trail to find the parking lot closed to cars and groomed for snowmobiles. The only way to access it is from the snow park over a mile down the road, and there's nowhere to buy a permit at the site or in town, so plan ahead! A helpful community shop told us the closest place to buy them was Cle Elum - I think they're available online as well. Some cars were parking on the road, but we saw a deputy handing out tickets. We asked and were told you can only park there with winter rec permits - looks like they're meant for snowmobiles.

Rather than spend the rest of our day driving around to find a permit, we opted to just find another trail close by.

This is mostly a snowmobile destination, so be prepared. The pictures look peaceful, but we never quite got away from the noise, even though the trails spilt apart around 1/4 mi. The snowmobiles are just on the other side of the river, and we could still hear them all day.  

We kept slogging all the way to the lake, and were sadly disappointed when we got there, as it is right off the snowmobile track. While we were the only snowshoers who made it that far, it wasn't the solitude we hoped for. The GPS only said 844 ft gain, but the trail goes up and down so many times, it probably amounts to 1600 feet climbed. It was a ton of work for not a lot of payoff.  The three other people we saw on the trail past mile 2 or 3 were carrying their snowshoes, and walking the trail in boots. The snow is packed enough, I guess you don't even need snowshoes.

That said, since it is less crowded than a lot of other trails, I would recommend going a shorter distance, enjoy some solitude past mile 2 or 3, find a nice spot for lunch and turn around. Don't bother slogging to the lake, unless you are after mileage.