Ah yeah I totally forgot NASCAR, which I believe I've heard is right up there with American Football in popularity.
I've always liked the regional differences as it's fun to see different sports remaining alive and well, such as the reemergence of Lacrosse. Of course, Florida is mostly just obsessed with American Football (and obviously some NASCAR/NBA), which has lead me to severely disappoint people I've met from farther north when I'm forced to admit that I know next to nothing about Hockey.
Uh, no. Absolutely not. NASCAR isn't near top 5 in popularity. I would even suggest it's behind Soccer and Hockey.
Well I would have assumed the same but, much like country music, it's apparently hugely popular in circles I'm not as familiar with.
This 2012 article from Forbes says that it has the largest fanbase in the US at approximately 70 million, has by far the most spectators attending its races of any sport, and had $3 billion in sponsorships, almost doubling the NFL.
By almost any measure, it's actually the most popular sport in the country: