As some of you may know, there is 8th, 9th, 11th and 12th...but no 10th street! 9th and 11th are exactly one city block apart, too, so 10 was skipped. (Across the river, "10th" could maybe be Taylor street). Any historical reason for this? A lot of googling hasn't come up with a satisfying answer.
The short answer is that 7th, 8th, 9th, and 11th streets were given numbers rather than their original names long after the streets were built, and the numbers were assigned to best align with the city's new addressing scheme based on State and Madison, a scheme adopted in 1911 for the downtown area. Taylor was already established at 1000 South (from State Street west), and 9th was a little north of Taylor and 11th a little south.
Unlike New York, where the street grid for the entire island of Manhattan was laid out in advance, Chicago's streets were built in fits and starts, as property was developed, subdivided and annexed to the city. What we today know as 7th (Balbo), 8th, 9th, and 11th Streets were originally named Hubbard Ct., Peck Ct., Eldridge Ct., and Harmon Ct. Streets on the South Side were renamed with numbers around 1868, and they began with 12th Street. The reason for that is still unclear, but it probably was that it was (more or less) twelve blocks south of the river, the north-south dividing line at the time. House numbers did not coincide with street numbers until 1879, when Chicago adopted the "Philadelphia plan" of matching block numbers for the area south of 12th Street. (New York and San Francisco never adopted this logical addressing system).