As Apple’s mobile App Store turned 1 year old this past week, the Cupertino company announced Tuesday that more than 1.5 billion total applications were downloaded in the last 12 months, and the store’s popularity continues to grow at an incredible pace.

That’s another half-billion downloads in the last three months – a trend which suggests the App Store’s popularity is gaining significant momentum.

On April 23, the App Store hit 1 billion total downloads, just over nine months after the destination first launched on July 10, 2008. Over those first 288 days, the App Store averaged nearly 3.5 million downloads per day.

But serving up an additional half-billion applications since April 23 has skewed that total much higher. Over the period of one year, Apple’s App Store has been home to nearly 4.1 million application downloads per day.

To put the last three months in perspective, to achieve 500 million application downloads since April 23, Apple has maintained a pace of over 6.3 million downloads per day over the past 79 days.

Chalk it up to more than 40 million devices capable of accessing the App Store in consumers’ hands. The three iPhone models and the iPod Touch serve customers in 77 different countries.

“The App Store is like nothing the industry has ever seen before in both scale and quality,” said Apple chief executive Steve Jobs. “With 1.5 billion apps downloaded, it is going to be very hard for others to catch up.”