My current house cat, Parker Prettykoshka, was born outside in the shed as a feral. This is the story of how I was able to tame her.
First, I began being friendly to the shed cats and kittens long before Parker was born. At one point in the litter before her, all four kittens were lap cats; their mother Smudge even jumped up into my lap when they all were there and nursed the kittens in my lap. Parker, her littermates, and the other kittens of her class knew my lap; at one point, I had all ten or eleven kittens and Smudge on my lap on one cold morning. So you may claim that she was not entirely feral, even though she was an outside-only cat.
When Parker was about eight months old, I took Parker, her littermate brother Butler, Inky, and Inky's littermate Truffles to Protect Every Pet to be fixed and get a rabies shot.
My plan was to take both Parker and Butler with me when I left the farm; as posted elsewhere on this site, Butler did not survive his second summer and never got the chance to leave the farm.
I called various vets for advice on converting my outside only cat to an inside only cat. They seemed to think that she was still young enough to do make the move. I also had the recommendation that I could move my everything into the apartment and come back for the cat the next weekend; that is what I did.
One of the recommendations was to prepare the apartment with a Feliway diffuser so it would not smell so bad when she arrived. I did that, and had the litterbox filled before I left to go get her off the farm.
The morning we left the farm, I picked her up at breakfast and put her in the carrier. We then stopped at a vet in the county seat, which was about where I would get on the interstate anyway. The vet gave her a quick examination, and some sleeping pills so she would not be so upset during the trip (about a five-hour drive). He also gave me a dose of Frontline to give her to get the fleas and ticks off.
When we got to the apartment, I put her in the bathtub of the second bathroom, where her litterbox was and where I would feed her. I let her out of the carrier and applied the Frontline. When the medicine took effect, the ticks almost ran off of her. I squished those I could see in the tub. I also introduced her to Friskies indoor canned food; she perked up at the nice-smelling food.
She stayed in the bathroom a little over a week. I spent time in there with her after feeding her to get her accustomed to a smaller area ; 900 square feet is a lot more than 40 square feet, but a lot less than the 400 acres, or however big her territory was, on the farm. After about a week and a half, I let her out, and she began sleeping with me.
However, she was getting bored. She would chase her tail for amusement, and wake up about 2:00 or 2:30 in the middle of the night for exercise. I finally took her to my current vet, a behavioral specialist, who had a few suggestions. One was that I should play with her in the evenings every night to get all her energy out. Another was that I should spread her dry kibble around the house so she would have to search for it. With those small changes, she got so she slept through the night.
She still likes to sit by open windows, and will occasionally try to bolt out the door if I leave it open too long when I come in, but she is on the whole happy with being an inside cat. If the birds wake up before sunrise, however, she will wake up as well.
The new apartment has frosted windows in the front bedroom, since it looks out onto the common porch/balcony. I built her a tower of boxes so she can jump up and look out the clear glass at the top, and she spends a lot of time up there.