While there, Tara found a sense of security, and enjoyed the riches Maryann offered. There was always an endless amount of exotic foods, wine and marijuana. Maryann's home was also the site of various parties and orgies. Maryann later claimed to Tara that the house, in fact, was not hers and that she had been watching it in the stead of one of her clients who was away in Peru.
This was a ruse so that she could remain close to Tara and continue to manipulate her.
Given that Maryann was shown to quickly move in and claim the Stackhouse home as her own, and given that Eggs mentioned Maryann's nomadic lifestyle, this house, was likely once in the possession of someone else who, no doubt, met an unfortunate fate.
This was likely one of several houses that Maryann acquired including the one where Sam first encountered her in his youth.
The home is located in Pasadena, CA. It’s about two miles east of the famous Huntington Library & Gardens (in San Marino), and about a mile and a half west of the Santa Anita Race Course and the L.A. Arboretum. (All three of those places have been used extensively for filming, over the years.) The producers also used the back yard, the pool, the patio, the interior of the house and even the same furniture (e.g. the bed Tara wakes up in the next morning.)