Population 1 (the camp caretaker); Elevation 4,600 feet (1,400 meters)
Camp Mather is a summer camp owned and operated by the city of San Francisco. It runs from mid-June through mid-September, more or less, and if you're a resident of San Francisco (or an extremely lucky non-resident), you may be able to win the lottery to reserve a week's stay.
It's not likely, though. The real Camp Mather action for Yosemite visitors is the separately owned Evergreen Lodge, located just outside the camp. It has a collection of cabins and tents accomodating from 2 - 6 people, with rates ranging from $80 - $380 per night. It also has a bar and dining room and hosts a variety of activities ranging from massages to fly fishing expeditions.
Another mile farther back toward Highway 120 is the Dimond O Campground, a forest service facility with campsites at $21 per night for single-family units; roughly a third of the 36 campsites are awarded on a first-come, first-serve basis. Dimond O campers can use showers at the Evergreen Lodge for a $5 fee and the outdoor recreation facilities at Camp Mather for $10/day (Evergreen Lodgers can also take advantage of the latter offer).
Con: The cabins at the Evergreen Lodge have a dark past: they were originally built to house workers constructing the dam that blotted out Hetch Hetchy Valley, one of the most infamous episodes in Yosemite history. On the other hand, they've also served as a moonshine distillery and a brothel in the 80-some years since they were built. We all have our ups and downs.
The Evergreen Lodge hosts a variety of outdoor activities, from guided hikes to naturalist tours to fly-fishing trips. There's also a masseuse on staff.
Camp Mather has a swimming pool, lake, tennis courts, and a beach volleyball court; non-campers can get access to them for a $10 daily fee.
Camp Mather is perhaps most famous for hosting the Strawberry Music Festival, a series of bluegrass concerts on Memorial & Labor Day weekends. Tickets can sell out months ahead; check early if you want to attend.