How many people volunteer in the United States?

Hello.

Approximately 84 million to 111 million people in the United States
volunteer.

Here are some estimates:

"More than half (54%) or 111 million Americans volunteered in the past
year—a record number."
Source: Pew-Partnership.org
http://www.pew-partnership.org/pubs/rwa/summary/engaged.html

"An estimated  83.9 million adults formally volunteered approximately
15.5 billion hours in 2000."
Source: Independent Sector: Volunteering in America Fact Sheet
http://www.independentsector.org/media/volunteering.html

"109 million people reporting they volunteered an estimated 19.9
billion hours"
Source: Independent Sector
http://www.independentsector.org/media/voltimePR.html

Also see Independent Sector's "Giving and Volunteering in the US 2001
Key Findings", in PDF format (Adobe Acrobat is required)
http://www.independentsector.org/PDFs/GV01keyfind.pdf

Here is a statement made by a policy committee in the United States
Senate:
"90 million Americans perform volunteer work in some capacity"
http://www.senate.gov/~rpc/rva/1061/1061286.htm

search strategy: "million americans", volunteer, volunteered

I hope this helps.

The number varys because much of the volunteering is informal, and
some pressure is applied to voluteer in other cases so the person may
not think of it as "volunteering" If you count borderline and minor
efforts and good intentions that went poorly, it could exceed 95%  
Neil