Got it, like most of you, from Howard Cosell on MNF (was watching it at home on Channel 7, and it was actually past my normal bedtime). Needless to say, IIRC it was a no-brainer lead story for us next morning, saturation coverage, and Jeff Kaye, who had a long history as a rock radio personality and programmer, wove well crafted tributes into our morning show.
Lennon was relevant to all of us on a number of levels. For some of us he was the staple of the programming we'd been doing for years. For some of us (myself included) we'd grown up with his music from the 1964 Ed Sullivan show appearances onward. And he was very much a part of the present at the end of 1980 as well. For my part, his post-Beatles music, starting with the "Imagine" album, was Lennon at his creative best. To give you an idea of how contemporary he was for young adults, two cuts from his Double Fantasy album (Starting Over and Woman) were already in our hot rotation at WBEN when he died and that was also true crosstown at WGR and at KB--we lost not just a part of our past but a part of our present that night.
Anniversaries of sad events like this make you think about what might have been--sure, John Lennon's creative legacy was already big, he'd already helped reshape our culture and to a degree, our way of thinking about and looking at the world. But he had just turned 40 when he was taken, and I remember what my boss, the late Jim McLaughlin, said that Tuesday morning---" I wonder what we missed, what he might have given us next?"