Allegheny County, Pennsylvania, is one of very few (and apparently the most populous) to publish data on its dog registrations. Nathan Fulton, a student at CMU, offers a summary of Pittsburgh Doggos By the Numbers, though it should be noted that it excludes those within city limits. (With 300k humans in town and a million more out in the burbs, assume we're missing at least a quarter of the doggos)
Ten Most Popular Dog Names in Allegheny County Name Count Bella 708 Lucy 474 Buddy 469 Molly 435 Bailey 424 Sadie 398 Max 393 Daisy 370 Charlie 328 Cooper 305