Linkin Park had the best-selling US album in 2001
CD-copying, internet swapping, a weak economy and other popular forms of entertainment such as DVDs and video games have been blamed.
Rock band Linkin Park enjoyed a surge in popularity over Christmas to make their CD Hybrid Theory the most popular album of the year in the US.
Hybrid Theory overtook Shaggy's Hotshot, which had been expected to be the year's number one.
A total of almost 763 million albums were sold in the US in 2001 - compared with almost 785 million in 2000, Soundscan statistics reveal.
Internet downloading from Napster-like sites and CD-copying - or burning - are still seen as major threats to sales.
A recent industry study found that half of those questioned had downloaded music from the internet in the last month, and 70% of those had burnt songs onto CD.
"The market is fragmented because of people spending more entertainment dollars on other things like video games," entertainment lawyer Jay Cooper said.
"There was also a strong impact from the weaker economy and free online services."
The slump comes despite the fact that the price of CDs has not risen as quickly as other forms of entertainment in recent years.
In November, trade body the Recording Industry Association of America (RIAA) released figures comparing the cost of a CD with concert, cinema, theatre and sports tickets, books, cable TV and video rental since 1993.
The average suggested list price of a CD rose from $13.14 (£9.13)to $14.02 in eight years (£9.74) - this is in fact a drop of 12% when inflation is taken into account, according to the RIAA.
The US accounts for 40% of world CD sales. Most other countries have also seen declines, with only the UK and France posting increases.
UK album sales rose by 5% in the first nine months of 2001.
In Germany, the decline is said to be the worst for 20 years.