Our oldest son's birthday is in the middle of May and we've found this to be the perfect time for an outdoor get together on the lake at Shawnee Mission Park with our friends and family. Several times, we've rented a shelter here (specifically Shelter #7 as it's one of the bigger 'Small' shelters with a capacity of 56 and sits right on the lake) and everyone always has a terrific time! The rental fee for a Johnson County resident for 1/2 day is only $35 - quite a bargain in my opinion - as this includes 6-7 hours reserved time, 7 tables, 2 grills, and the electricity and lights. You can bring your own food, decorations, etc... and really customize the party too!
http://jcprd.com/parks_facilities/map_shawnee_mission.cfm
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