Judge Rose said there had been “an abuse of trust – you are trusted by young fans to behave properly”.
He said: “She had only just turned 15 when you began grooming her, because, as you were to admit, you found her sexually attractive.”
At the start of his trial last month, Johnson had admitted grooming the girl and one charge of sexual activity. He was found guilty of sexual touching and cleared of one charge relating to another sexual act.
Judge Rose said Johnson had had “every opportunity” to enter guilty pleas to the charges he finally admitted. He ordered the footballer to pay £50,000 of the prosecution’s £67,132 costs.
Earlier, Dr Philip Hopley, a consultant psychiatrist giving evidence for the defence, told the court: “This is a man who, at the age of 28, is socially and psychologically immature.”
The doctor said he found no evidence in Johnson of an attraction to pre-pubescent children or “sexual perversion”.
Speaking after Johnson was sentenced, Det Insp Aelfwynn Sampson, of Durham Police, said: “Fame, celebrity and a position of power does not give you the right to break the law in pursuit of whatever you desire.
“This girl should have been safe but she was used by the public figure she looked up to most.”
Outside the court, Gerry Wareham from the Crown Prosecution Service, said: “Adam Johnson exploited a young star-struck fan, actively grooming her over a number of months in single-minded pursuit of his own sexual gratification.”
Earlier, the court was told the player had lodged an appeal against his conviction for sexual activity with the girl.
He is due back in the dock this afternoon.
Johnson began his career at Middlesbrough before moving to Manchester City and then on to Sunderland in 2012.