Authorities said a tip led them to the cats, where they were found in crates in a storage locker that measures about 600 square feet. They also said 36 cats were found dead.
Officials said the conditions were unsafe and crates were stacked on top of one another. They were found to have been fed recently, but litter boxes still contained waste.
"They were found in crates, they were found in containers, there were cats found in a chain-linked area and there were free-roaming cats as well," said Ricky Whitman of the Pasadena Humane Society. "They were absolutely everywhere."
The woman who allegedly put the cats in the storage facility, Tanya Regan of Temple City, has been cited. People at the home refused to comment.
Meantime, the cats are being taken care of at the Humane Society, where about 150 cats are already living.
Rafael Martinez, who owns an auto shop next door to the storage, said he had to build a makeshift wall to keep the smell out, but it didn't work.
"It was terrible," Martinez said. "Now we are freely smelling fresh air. Sometimes I wanted to vomit."
The Humane Society said this is the worst case of animal hoarding in its 108-year history.
With the addition 240 cats, the Humane Society is overwhelmed, but they said they would care for all of them.
"This is an expensive situation for us," Whitman said. "We will be housing these animals until the court case is resolved. It could be six months to a year that they will be housed here."
Investigators are looking to see if charges will be filed against Regan.