Dash Point State Park (5700 SW Dash Point Rd.) is in Federal Way, five miles northeast of downtown Tacoma [1] on Puget Sound, on Highway 509, a.k.a. Dash Point Road. On Sound side of the park there’s a beach (the water here is warm enough for swimming—or at least wading—in summer), picnic tables, and trails that lead to the water.
Links:
[1] http://www.moon.com/destinations/washington/south-puget-sound/tacoma