There is no doubt that Atticus influenced Maycomb. The influence might not be as strong as we would like, but he has made an impact.
First, Atticus made an impact on Mr. Cunningham. For example, Atticus helped him with legal matters, even though Mr. Cunningham was not able to pay money. This is why he came around and gave Atticus food instead. This generosity of Atticus had an effect. Similarly when Atticus stood up to the mob, he showed great courage and conviction. Eventually the mob turned aside and Mr. Cunningham was part of that mob.
Second, Atticus influenced the black community. The black community honored him. In one of the my favorite scenes in the book, reverend Sykes tells Scout to stand up, because Atticus was passing by. The blacks knew that they had a champion in Atticus.
Finally, other citizens of Maycomb were influenced. In a insightful dialogue Miss Maudie makes this point. Look for the words, "baby steps." A quote is here is apropos.
"His colored friends for one thing, and people like us. People like Judge Taylor. People like Mr. Heck Tate. Stop eating and start thinking, Jem. Did it ever strike you that Judge Taylor naming Atticus to defend that boy was no accident? That Judge Taylor might have had his reasons for naming him?"
This was a thought. Court-appointed defenses were usually given to Maxwell Green, Maycomb’s latest addition to the bar, who needed the experience. Maxwell Green should have had Tom Robinson’s case.
“You think about that,” Miss Maudie was saying. “It was no accident. I was sittin‘ there on the porch last night, waiting. I waited and waited to see you all come down the sidewalk, and as I waited I thought, Atticus Finch won’t win, he can’t win, but he’s the only man in these parts who can keep a jury out so long in a case like that. And I thought to myself, well, we’re making a step—it’s just a baby- step, but it’s a step.”