I grew up with and went to high school with a professional golfer who has won several major tournaments on the PGA tour and whose name many would recognize.
My brother is a better person to ask this question though - he is also a pro golfer (he is still close friends with this guy we went to high school with) and knows a lot of other professional golfers as well - including Jack Nicklaus (my brother and Jackie Nicklaus were college roommates at Chapel Hill). My brother also knew a lot of other athletes who were at Chapel Hill at the same time as he was - one of which was Michael Jordan.
But me personally? - only the one pro golfer. Unless you count:
Iditarod mushers. I knew several of those guys when I lived in Anchorage. Those guys are celebrities...but really only in Alaska.
Tommy Moe - Olympic Downhiller and Gold Medalist. I was in a bike racing club with him in Anchorage and chatted with him a few times at various club-related events. But I wouldn't say we were 'friends' or anything. Met him more than once...but it was all within the confines of the Arctic Bike Club activities.
EDIT after reading other people's posts:
Now, if we are talking about 'brushes with greatness' where you only met the person once...that is an entirely different matter. My two most famous brushes with greatness are:
Bruce Springsteen (I had backstage passes at one of his concerts and got to talk with him for a while)
Former President Jimmy Carter (met him at one of his book signings here in Atlanta)
In addition to these, I've met several other best-selling authors at book signings and actually partied with the crew of Airforce One in Moscow, circa 1995 (then-President Clinton was in town for the major VE Day anniversary).
And then there are all the scifi actors met at cons - the usual suspects - everyone from Shatner to David Boreanaz.
But IMO, 'brushes with greatness' such as these are not the same as knowing someone/growing up with someone.