The carnival was Dill Brothers Combined Traveling Shows, and the hometown was Waukegan, Illinois. The time was the autumn of 1932.
His meeting with Mr. Electrico (quite literally!) sparked his imagination, and this autumn carnival was an exotic stimulus, but wholly benign.
However, it's clear to me that in Bradbury's fiction, the autumn carnival of his youth was transmuted into the fearfully malevolent Cooger and Dark's Pandemonium Shadow Show, in the novel Something Wicked This Way Comes.
This is the cover from the film version, for which Bradbury wrote the screenplay, and with which he was quite pleased.