Major Religions of the World
Ranked by Number of Adherents (2002)

1. Christianity: 2 billion
   
2. Islam: 1.3 billion
   
3. Hinduism: 900 million
   
4. Secular/Nonreligious/Agnostic/Atheist: 850 million
   
5. Buddhism: 360 million
   
6. Chinese traditional religion: 225 million
   
7. primal-indigenous: 150 million
   
8. African Traditional & Diasporic: 95 million
   
9. Sikhism: 23 million
   
10. Juche: 19 million
    
11. Spiritism: 14 million
    
12. Judaism: 14 million
    
13. Baha'i: 6 million
    
14. Jainism: 4 million
    
15. Shinto: 4 million
    
16. Cao Dai: 3 million
    
17. Tenrikyo: 2.4 million
    
18. Neo-Paganism: 1 million
    
19. Unitarian-Universalism: 800 thousand
    
20. Rastafarianism: 700 thousand
    
21. Scientology: 600 thousand
    
22. Zoroastrianism: 150 thousand

Source

* many atheists/ agnostics undoubtably respond with 'non-religious/ secular' due to the stigma of 'atheism'

source

Collection of polls showing population of Atheists, Agnostics, Secularists and Non-Religious

Poll	Date	Group	Adherents	%	total pop.	Source
The Universal Almanac	1990		Atheist	9.9%	210,500,000	Universal Alminac+
			Non-Religious	16.9%	805,900,000
Breakdown of world religions	1989		Nonbelievers	21.6%	1,100,000,000	Catholic News Service and Encyclopedia Britannica+
Major Religions of the World Ranked by Number of Adherents	2001		Secular/Nonreligious/ Agnostic/Atheist	*	850,000,000	Adherents.com
United Kingdom Gallup - Telegraph	1999	UK 16-25 age-group	Atheist/ Agnostic	40%	*	Gallup - Telegraph
Major religious denominations, Canada	2001	Canada	No Religion	16.2%	4,796,325	Major religious denominations, Canada, 1991 1 and 2001
U.S. Religious Affiliation, self-identification,	2002		Atheist	1%	*	Pew Research Council
			Agnostic	2%	*
Top Twenty Religions in the United States, (self-identification)	2001		Nonreligious/Secular	13.2%	27,539,000	ARIS
			Atheist	0.4%	902,000
			Agnostic	0.5%	991,000
Non-Christian Religious Adherents in the United States	2000		Atheist	0.3%	925,000	Britannica Book+
			Non-Religious	8.8%	24,554,000

Atheist Prison Population

Other Groups

National Academy of Sciences	1998	members of the National Academy of Sciences	Personal disbelief in god	72.2%	517 members, half responded	Nature
			doubt or agnosticism	20.8%
Religious Affiliation US voters	2000	U.S. Voters	Agnostic or Atheist	7.1%	*	Harris poll
			Nonreligious/No answer	10%	*
What religious or nonreligious group doesn’t share your vision of American society	2003		Atheist (Muslims were second)	54%	*	American Mosaic Project

* No data given
+ Collected from secondary source

source

Divorce rates by religion (U.S.)

The Associated Press computed divorce statistics from data supplied by the U.S. Census Bureau and the National Center for Health. They showed that the highest divorce rates were found in the 'Bible Belt'. "Tennessee, Arkansas, Alabama and Oklahoma round out the Top Five in frequency of divorce...the divorce rates in these conservative states are roughly 50 percent above the national average" of 4.2/1000 people.

Conclusions

• The world population of non religious** ranges anywhere from 850 million to 1.1 billion making up 15 to 26.8%.
• The US population of non religious** ranges anywhere from 25 to 30 million making up 9 to 15%.
• If the US Prison Population statistics are accurate then there are far less nonbelievers in the prison system. This can be interpreted in many ways. Note that religious conversion is very active in prisons.

** the ambiguous term non religious as used above includes those identified as atheist, agnostic, secular, nonbeliever and non-religious as defined by those responsible for the polls and statistics.