I said mostly Austin, because Brian goes back to California a few times to visit his parents. Mainly because the book is about Karen. Also, there are a few scenes in Sunset Valley, which is technically not a part of Austin even though it is surrounded by Austin. The married couple also stop in Hildesheim, Germany for a night.
After the wedding Karen moves into Brian's place on Mt. Bonnell Road near Dry Creek Cafe. If you read Where Love Once Lived, you know this is the place where the Combine rented a cabin when they were students at the University of Texas back in the 1970's.
There are scenes at the Austin History Center, a fictional law office on Congress Avenue, Allandale mall and references to the Austin Public Library, Travis County Courthouse, Wooldridge Park, MoPac, 35th Street, Sun City Texas, Georgetown, Thundercloud Subs and Dr Pepper, a Texas favorite.
Several scenes take place in Clarksville, where Brian's best friend Phil lives with his wife Kay. His dad George, who played a prominent role in Where Love Once Lived, lives in an apartment out back and manages to help Karen in Love Lives On.