Atheist in the world

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

(self-identification, ARIS)

Religion	1990 Est. Adult Pop.	2001 Est. Adult Pop.	% of U.S. Pop., 2000	% Change 1990 - 2000
Christianity	151,225,000	159,030,000	76.5%	+5%
Nonreligious/Secular	13,116,000	27,539,000	13.2%	+110%
Judaism	3,137,000	2,831,000	1.3%	-10%
Islam	527,000	1,104,000	0.5%	+109%
Buddhism	401,000	1,082,000	0.5%	+170%
Agnostic*	1,186,000	991,000	0.5%	-16%
Atheist*		902,000	0.4%
Hinduism	227,000	766,000	0.4%	+237%
Unitarian Universalist	502,000	629,000	0.3%	+25%
Wiccan/Pagan/Druid		307,000	0.1%
Spiritualist		116,000
Native American Religion	47,000	103,000		+119%
Baha'i	28,000	84,000		+200%
New Age	20,000	68,000		+240%
Sikhism	13,000	57,000		+338%
Scientology	45,000	55,000		+22%
Humanist	29,000	49,000		+69%
Deity (Deist)	6,000	49,000		+717%
Taoist	23,000	40,000		+74%
Eckankar	18,000	26,000		+44%

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

source

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

Canadian Prisons	1925	Ca. prisoners	Atheist/ Agnostic, non-religious Uniterain	0%	0 of 1,2061	Steiner and Swancara
Prison Population executed for murder at Sing-sing	1925	US Sing-Sing Pen.	non-religious	0.33%	*	"The New Criminology," Max D. Schlapp and Edward E. Smith
Prison Population	1925	US Prisoners	convicts without religious training	0.1%	*	"The New Criminology," Max D. Schlapp and Edward E. Smith
Prison Population	1997	U.S. Prisoners	Atheist	0.209%	156 of 74,731	Federal Bureau of Prisons +

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

Christianity sinking; "none of the above" rising

* No data given
+ Collected from secondary source