"I've had 31 years to think about this, so, there is no nervousness, not the least bit of fear," Johnson said.
The donor is Johnson's 25-year-old son, Daniel. Johnson plans to spend the evening with his son before their procedures.
"With a living donor kidney transplant, if the kidney works right away recovery is actually pretty quick," said Dr, Ed Hollinger.
Ed Hollinger will place the healthy kidney into Johnson.
"He'll have two of his own and then the kidney transplant," he explained. "We don't actually take one of the kidneys out when we do a kidney transplant."
Within a matter of days the doctor said Johnson may feel like a new person.
"Often patients don't realize how sick they were, how badly they felt. When kidney function comes back quickly they feel pretty good," Hollinger said.
Johnson said he is leaning on his faith through this experience.
"I read the book of Job all the time. I read the Bible, but the book of Job is my favorite. If he can do that, this is a piece of cake for me," Johnson said.
Johnson said he had been very private but now feels sharing his experience is part of his public service.
"There have been people that walked up to me on the street and said, 'Because of you, my relative got a kidney.' And that's a great feeling. If you can help somebody else, it was worth it," Johnson said.
The 57-year-old said he now sees things differently.
"I was looking out the car window and actually paid attention to the people walking down the street, the kids playing. It really makes you appreciate life," Johnson said.
At Tuesday's police graduation, Mayor Rahm Emanuel publicly wished him well.
"Our prayers are with you tomorrow and a speedy recovery and I want to thank you for your service," Emanuel said.
Johnson expects to be hospitalized for a few days after the transplant and be off work for six weeks before he returns to his work as a public servant.