Beautiful but very popular
These coordinates are one of the first sites on the right, when arriving from Two Pan Trailhead, but there are dozens around the lake if you follow the trail.
This was my second time backpacking in the Wallowas, and my first time at Mirror Lake. The lake is big with lots of dispersed sites, but when we arrived on Friday evening we felt lucky to find a place. (Some folks resorted to camping on vegetation areas—please don't do this!) The lake was so full and the sound carried over the water so much that you could hear conversations. Luckily it seemed to clear out by Saturday morning, for whatever reason.
We clocked the hike in from Two Pan Trailhead at 7.3 miles. The incline is mostly gradual with a nice break of mostly flat trail in a beautiful valley meadow area. Lots of horse traffic on this trail, so watch your step! The lake is super clear, and worth a swim. The trail to summit Eagle Cap is close by and a great day-hike for amazing views.
If you're looking for a secluded place in the Wallowas, I would head elsewhere. If you want an easy backpack in, and don't mind being around lots of other people, Mirror Lake is a great choice.