It seems that the question is looking for textual evidence for where Harper Lee's novel To Kill a Mockingbird takes place. In chapter one of the novel, Scout Finch is giving the background of her family. Scout states that her family are Southerners and that Simon Finch (a trapper) established Finch's Landing forty miles from the Alabama River. Scout states that the men of the Finch family were to stay in Finch's Landing. Her father, Atticus Finch, is the only male to have stayed (his brother went to Boston for medical school).
The following section, the seventh paragraph of chapter one, states the town and county Atticus and his children (Scout and Jem) reside in.
When my father was admitted to the bar, he returned to Maycomb and began his practice. Maycomb, some twenty miles east of Finch's Landing, was the county seat of Maycomb County.
Therefore, this excerpt from the chapter provides the textual evidence needed to state where the novel takes place. The novel does, in fact, take place in Maycomb, Alabama.
Although Maycomb, Alabama, is a fictional town, in chapter one Harper Lee provides some geographical information to help the reader locate its whereabouts. Saint Stephens, Alabama, is a real town, located about 70 miles north of Mobile. Atticus's ancestor, Simon Finch, settled 40 miles north of Saint Stephens, or 110 miles north of Mobile along the Alabama River.
So Simon ... bought three slaves and with their aid established a homestead on the banks of the Alabama River some forty miles above Saint Stephens.
The Finches continued to live on that original homestead, called Finch's Landing. During the novel, Scout's Aunt Alexandra still lives at Finch's Landing. When Atticus studied law, he went to Montgomery, Alabama, which is 150 miles northeast of Saint Stephens. When he passed the bar exam, he returned home, but in order to practice in the county seat where the courthouse was, he moved to the town of Maycomb, which is 20 miles east of Finch's Landing. Maycomb County and the town are fictional. The actual county for Saint Stephens is Washington County, and the actual county seat is Chatom. Lee writes:
Maycomb, some twenty miles east of Finch's Landing, was the county seat of Maycomb County.
Harper Lee grew up in Monroeville, Monroe County, Alabama. It is close to where her fictional town of Maycomb would be located if it were a real place. Because of Harper Lee's fame, Monroeville has become a tourist attraction and is known as the Literary Capitol of Alabama.