Upper McKinney Falls is the closest real swimming hole to downtown Austin that isn't Barton Springs, and on a hot afternoon it can be the better choice. Onion Creek pours over a broad lip of Cretaceous limestone into a deep green pool ringed by sculpted rock, with room to spread a towel on the slabs and a shallow shelf for kids at the downstream end. The falls are a five-minute walk from the Upper Falls parking area inside McKinney Falls State Park, at 5808 McKinney Falls Parkway, about 13 miles southeast of the Capitol. The park opened April 15, 1976, and drew 283,523 visitors in 2025; the falls are where most of them ended up.

Texas Parks and Wildlife charges $6 per adult to enter, and kids 12 and under are free; day passes sell out on spring and summer weekends, so reserve online. The gate is open 8 a.m. to 10 p.m. Swimming is allowed at both the Upper and Lower Falls at your own risk, with no lifeguard. The park's rules for the water are specific: no food, alcohol, glass or coolers in the swim areas, no speakers, and dogs stay out of the creek. After heavy rain Onion Creek goes brown and fast and the park closes the falls until it drops, sometimes for days, and low summer flow can bring bacteria advisories; the park posts both at the entrance.

The geology is why the pool is here. The falls formed where Onion Creek cut through a layer of volcanic ash from Pilot Knob, an 80-million-year-old submarine volcano whose cone is visible a couple of miles east, faster than it cut the harder limestone around it. The same rock holds Smith Rock Shelter, a National Register site where people camped for thousands of years, and the ruins of Thomas McKinney's 1850s homestead and gristmill along the Lower Falls trail. A section of El Camino Real de los Tejas, the Spanish colonial road, crosses the park.

There is more here than the swim. Nearly nine miles of trail wind through the 744 acres, including the paved 2.8-mile Onion Creek Hike and Bike Trail that loops both falls and is good for a family bike ride, and rougher singletrack on the Homestead and Flint Rock loops for mountain bikes. The campground has 81 sites with water and electricity and six cabins, all reservable, which makes this an easy overnight for a swim in the evening when the day crowd has gone home. Bring water shoes; the limestone is slick where it's wet and sharp where it's dry.