There was a time (roughly 1972-1979) when his music was an important element of album rock radio, as were many other folk-based singer/songwriters of the era.
Here's three Dan Fogelberg albums that immediately come to mind - music I can recall playing on the air (as current) early in my career:
Of course there were many more. And as AOR evolved, AC radio became hip - and Dan's music became a staple of that format for many years. And every year about this time you can hear one of Dan's songs on radio stations from coast-to-coast:
Read more on Dan's passing here. Tipped by Radio Daily News.