Below is part of a well distributed 1872 map of Dallas that shows the Commerce St. Bridge. In the second full block east of where the Trinity was then located you find an image that seems to resemble the current Kennedy Memorial. It is on the north side of Commerce Street, just like the Kennedy Memorial location today. This 1872 map is from http://www.glo.texas.gov/history/archives/map-store/index.cfm#item/89080
This larger view below, of the 1872 map above, shows the name Commerce St. to the East end of Commerce Street. If you look closely you can see that Market Street is actually the 2nd street, an additional block east from this strange building shell.
The Kennedy Memorial is on Northwest corner of Market & Commerce as you can see in the image below. The Old Red Courthouse is on the location of the shell of a building from the 1872 map above. It was the unfinished new Dallas County Courthouse shell started in 1871 after the remains of the old courthouse were torn down. After the walls were built with $40,000 Dallas County allocated, they ran out of money. They did not get the money needed to finish this new courthouse building until the 1874 Legislature allocated the needed funds. See this Dallas Courthouse history at http://www.texasescapes.com/DallasTexas/Dallas-County-Courthouse-Dallas-Texas.htm#1872