The Friday file: After rising for decades, and peaking in ’06, the number of households with a pet fell between ’06 and ’11. The decline was due to the lousy economy and more Americans living alone. In ’91 there were 57 million pet cats and 52.5 million pet dogs. By ’06 there were 80 million cats and 71 million dogs. Today, it’s just 74.1 million cats and 69.9 million dogs.