Welcome to your first Ragbrai. There may not be one official starting point, as one park may not have room for all to camp. The last time I started from Sioux City I camped in Larson Park. At the west end of Larson Park Road is a boat ramp that is perfect for dipping back wheels. That is also the area where Larson Park Road bends to the north and becomes Hamilton Blvd. That is about as official starting point as I can think of. We took Hamilton and Outer Drive to get out of town. You might get onto Hamilton from a different park. Have fun!