WASHINGTON, Jan. 18 (RNS) -- Despite an upswing in the number of both Muslims and non-religious people worldwide, Christianity remains the world's largest religion, according to a new report on religious demographics.

"Christianity has become massively accepted as the religion ofdeveloping countries in the so-called Third World," said the 1,700-pageWorld Christian Encyclopedia, prepared by the Global EvangelizationMovement research center in Richmond, Va. The report details statisticalinformation about religious groups around the world.

The report pegged Christianity as the "most extensive and universalreligion in history," pointing out that Christians constituted thelargest religious group worldwide at both the start and end of the 20thcentury.

In 1900, Christianity boasted some 555 million adherents (32.2percent of the world's population then). In the year 2000, the religionclaimed 31 percent of the world's population with more than 1.9 billion followers.

The report noted that 386 million Christians identify themselves asmembers of "independent" churches distinct from Catholics, Protestants,Anglicans and Orthodox Christians. In the United States, 192 million people say they are Christians.

Islam followed Christianity as the world's second most-populousreligion, with 1.2 billion followers, some 19.6 percent of the world'spopulation. At the dawn of the century, Islam claimed 200 millionfollowers, about 12.3 percent of the world's population.

In the pastthree decades alone, the number of Muslims in the United States morethan quadrupled to 4.1 million.

Also increasing since 1900 is the number of people who identifythemselves as non-religious, the report found. Though 3 million saidthey were non-religious in the year 1900, last year that number stood at768 million -- 12.7 percent of the world's population.

Behind Islam and Christianity came Hinduism with 811 millionfollowers worldwide. Buddhism has 360 million followers around theglobe, while Sikhism and Judaism boast 23 million and 14 millionfollowers, respectively.

Acknowledging the lack of an exact consensus regarding thestatistics for non-Christian religions in the United States, the reportfound that Judaism has 5.6 million followers in the United States. Thatnumber drops to 2.4 million for Buddhists, and 1 million for Hindus.

Worldwide, the biggest decline in followers was found amongtraditional belief systems -- particularly in China and Africa.