No. 4.

I am composed of 18 letters, and commemorate an important event in American history.

My 4, 8, 18, 16 is a toy.

My 3, 14, 11, 1, 5, 6 is a word describing quantity.

My 7, 12, 15, 16 is a favorite place.

My 11, 2, 9, 10, 5, 13 is a plant.

My 10, 16, 17, 18 is a fast.

Edgar Seeman.