Elizabeth Johnson -- who at one point admitted to killing her son, the missing infant Gabriel Johnson, before saying she gave him away -- told a judge she "deserved the maximum" sentence, before receiving a prison term of 5.25 years, half of the max.
In October, Johnson, 26, was found guilty of custodial interference and unlawful imprisonment stemming from the disappearance of her 8-month-old son, last seen on Dec. 24, 2009. The baby's whereabouts remain unknown.
"I am brokenhearted over my son still being missing," said Johnson, wearing a striped prison jumpsuit. "I'm at a loss because I do deserve the max. What I have done is unconscionable. I would convict myself.
"I do deserve the maximum, I do," she said through tears. "[But it] wasn't how [the prosecution] made it out to be. It wasn't like that. That's all I have to say."
Judge Paul McMurdie said he wished he could design a sentence that would compel Johnson to disclose Gabriel's whereabouts, but could only "sentence her for the offenses [for which] she's been convicted."
Johnson, 26, will serve 5.25 years in an Arizona state prison, followed by four years of probation.
At today's sentencing hearing, prosecutor Angela Andrews called Johnson' actions "despicable," but said the state would drop its request to see Johnson serve out a maximum sentence if she would tell authorities where her son could be found.
Johnson, who has been in jail for the past three years, faced a maximum of 9.5 years in prison on the two convictions. In October, the jury did not reach a verdict on a third charge of kidnapping.
Before Gabriel's disappearance, Johnson had been embroiled in a custody battle with the baby's biological father, Logan McQueary. The couple differed on putting their infant son up for adoption. Johnson had wanted to, McQueary did not.
"I think Elizabeth should be held accountable for her actions, for making my son disappear," Johnson told the court. "She should stay in jail until Gabriel is found or be given the maximum sentence as possible."
While she was fighting with McQueary over custody of their son, Johnson left Tempe, Ariz., with Gabriel and traveled to San Antonio, Texas, on Dec. 18, 2009. Johnson failed to bring Gabriel back to visit with McQueary two days later, violating a court custody order.
Gabriel was last seen with his mother on Dec. 26, 2009. The following day, Johnson sent text messages to McQueary saying she had killed him. Johnson was recorded telling McQueary that she suffocated their son with a towel until he turned blue. She said she then put his body in a diaper bag and put the bag in the trash.
Later, Johnson told authorities she gave Gabriel to a couple she met in a park in San Antonio, though she has never named who she gave the child to.
ABC News' Alexis Shaw contributed to this report.