Totally legit little campground, not rest area, not a wide spot in the road, a campground: Lewis Park in Wheatland, WY.
Lewis Park is a free, city run public park with different activity areas, like a basketball court, soccer, Frisbee golf a playground and has several sites for RVs as well as a designated area for tent camping.
There is potable water, spigots in both RV and tent areas. I tested the spigot near the RV sites and it works. I did not fill up because
I didn't think the pressure was sufficient to for my filters to be effective. Potable yes. Usable in my rig without filtering, no.
Cell quality varies. My van has ATT wifi, coverage was very good. Verizon cellular was good enough to get online but could be a lot better and my back up phone, Mint (T Mobile) barely but did, get online. The camp sites are oriented north/south and my Starlink had a clear view of the northern sky with real good wifi.
Be aware however, horses are not allowed in the park and, a train went by at 9:35 am on a week day - there are a lot of trains in Wyoming, that's how the rest of the country gets all it's stuff - so if you're a late sleeper, there is that. So, leave your horses at home and get up to enjoy the Wyoming sunrise.
PS: as a public venue, Lewis Park gets regular patrolling by police. Not a bad thing.