Yes, today hip hop is 40 years old - as are most of it's fans these days ;-)
The birthplace of hip hop is generally regarded as 1520 Sedgewick Avenue , the Bronx, New York City. This of course was where Kool Herc held his first party which was to unveil to the world the process of spinning two copies of the same record to create a continuous loop for the dancers (b-boys). This party took place on August 11th 1973.
The "Cindy C" mentioned above as one of the "special guests" is none other than Herc's sister, Cindy who the party was actually organised by.
Some say hip hop is dead. I say they're just not looking hard enough. It's all around us, sometimes not appearing anything like it once was but it's there. The real hip hop will forever remain because we grew up with it and it is such a part of us that it will never die.
This is very recommended. From the Hip Hop & Politics blog