Located on Mainstreet near downtown Parker, this park includes a lighted softball field, a multipurpose field, a basketball court, two playground areas, an outdoor pool with slides and a variety of water features, a shade structure with tables, a lighted plaza area with tables and public restrooms. Electricity is available in the pavilion areas.
A historic sign can be found on the baseball backstop, the 20–Mile historic marker is located at O'Brien park and a decorative wall mural appears in the Keiffer's Crossing tunnel. In addition, O'Brien Park boasts “time stones,” a public art display, along with other art displays on a "rotating" basis.
O'Brien Park's gazebo serves as the backdrop for many Parker events, including outdoor concerts and the Mayor's Holiday Lighting.
In fall 2005, the Town purchased 5.64 acres directly northeast of O'Brien Park with the intention of eventually developing it as an extension of the existing park.