At least, it wasn't what I thought it would be. I've lived in the Northeast, and always knew there were some country music stations even in big urban settings. I just never guessed how popular overall the format has been. So perhaps my assumption says something more about me than about the radio business.
That said, until last year, country music had been the most popular radio format in the US, according to a New York Times article, "For Conservative Radio, It’s a New Dawn, Too" by Brian Stelter.
In 2008, news talk radio surpassed country music for the first time.
It's an interesting article, noting interesting implications. Well worth reading.