Most sources say this distance was 12 blocks. Even Jerry himself did in at least one published interview. In January 2007, I paid my first trip to Cleveland and measured it myself. It was actually exactly 9½ blocks—Jerry's house on Kimberley Avenue in the Glenville neighborhood of Cleveland was the 11th down on a street of 22, and Joe lived on a corner. Pulitzer-caliber investigative reporting? Hardly. But accuracy isn't always glamorous.
Speaking of which, in Superman literature, Jerry's street name is alternately written as "Kimberley" and "Kimberly." In fact, as of my research visit and almost certainly still today, the street signs themselves are at odds—the sign on one end is with "e" and the sign at the other is without.
My book does not name the street but I nonetheless wanted to know which was correct, possibly with the vague intention of using it as a blog topic one day. My contacts at both the Cleveland Public Library and the Cleveland City Planning Commission (invaluable men both) verified that the official spelling is...begin erupting into a heightened and sweaty state...Kimberley.
It was Kimberley in a 1940 city directory and it was Kimberley when Cleveland annexed Glenville in 1898.
This was far from the most exhilarating research discovery I made on that trip, but of course you don't start a story with the climax.
9/19/09 addendum: I'm told that the city has addressed this and now the signs on both ends of the street read "Kimberley."