If you are asking for a description of the specific location of the Maycomb County Courthouse, you can find it in Chapters 15 and 16. Scout describes the children's walk from the Finch house to the town square on the night when they join Atticus in front of the jail (Chapter 15). As the children walk past Mrs. Dubose's house, "there were eight more houses to the post office corner." From there, they could see that
... the courthouse was dark. A larger square of stores surrounded the courthouse square.
The courthouse sits in the center of the courthouse square, with another business-lined square (the town square) surrounding it. Scout describes the courthouse in detail when the children head to town for the trial (Chapter 16). Only the pillars remained from
... when the original courthouse burned in 1856. Another courthouse was built around them.
For a good visual aid for downtown Maycomb, check out the excellent eNotes Map of Maycomb at the link below.