The urban myths about this are a lot more entertaining than the truth. One example: J Street was nixed from the map because D.C. designer Pierre L’Enfant hated John Jay, the new nation’s first chief justice. Another: The founding fathers anticipated a future in which Malcolm X threatened white supremacy, so they nixed X Street to avoid riling up the masses. (OK, I just made that second one up.)
At any rate, according to Bob Arnebeck, author of Through A Fiery Trial: Building Washington, 1790-1800, the real answers are prosaic. There’s no J Street because, back then, typography had yet to be standardized, and I and J were often used interchangeably. Of course, notes Arnebeck, so were U and V. But, he suspects, those letters made the cut because L’Enfant was trying to get to the edge of his map without having to use “X,” a letter that in those days was often used to signify Christ. As for Y and Z, Arnebeck says, “I think they simply ran out of streets.” The original boundary of the city was what is now Florida Avenue, which rises just a block north of V.
Now, of course, we have plenty more streets, one of which has been renamed in honor of Malcolm X. Perhaps it’s time to remedy other cartographic non-insults by renaming some of the others for Y, Z, and poor old John Jay.