Sophie Smith's tail contains fur measuring 25.68 centimetres (10.11 inches) at its longest point.
The length of the fur surpasses that of the late former record holder and internet sensation Colonel Meow by more than an inch, Guinness World Records said in a statement.
Jami Smith, Sophie's owner from Oceanside, California, said she first met Sophie, thought to be just three weeks old, following a chance encounter with strangers.
"I was out walking my dog one Sunday afternoon when a truck drove up with a couple of guys in it. They stopped and held a small paper bag out of the window and asked if I wanted a kitten," Smith said.
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At first Smith considered taking Sophie to the local animal shelter but quickly changed her mind.
As Sophie grew, so did her fur, to the point where it began to seem quite exceptionally long.
"Her fur has always been long, especially on her tail. We would often comment on it. I even jokingly would say, It's got to be some kind of record!," Smith said.
"So one day for fun I went online to the Guinness World Records website to see if a record existed. And there it was. Colonel Meow with fur that measured 9 inches long!
Jami made an appointment at her local veterinary surgery Surfside Animal Hospital in Oceanside. Sections of Sophie's fur were removed and measured with witnesses on hand to verify the proceedings.