Kennewick police department facebook page says:

Now that summer is about here and it is getting warm out, KPD would like to remind everyone that city parks are closed 30 minutes past sunset till 6 am. The only exception to this is Lawrence Scott Park and the Southridge Sports Complex ball fields. These will stay open until midnight if the ball fields are being used. KPD officers have contacted several people in city parks after they were closed and verbal warnings were given. If you are found in a city park after they are closed you could be charged with criminal trespassing.