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The Gill Foundation is one of the largest funders of efforts to secure full equality for lesbian, gay, bisexual and transgender (LGBT) people in the United States. The foundation's mission is "to secure equal opportunity for all Americans, regardless of sexual orientation or gender identity and expression." 
The Gill Foundation was founded by Tim Gill in 1994, two years after the passage of Amendment 2, a Colorado ballot initiative denying lesbian, gay, and bisexual people equal protection under the law. As of 2017, the foundation had granted more than $335 million to various nonprofits.
In 2004, the Association of Fundraising Professionals (AFP), the largest association of charitable fundraisers in the world, honored the Gill Foundation with its 2004 Outstanding Foundation award.
The Gill Foundation is most known for its support of nonprofit organizations across the country working to bring about equality for LGBT people. Beyond its grant-making, the foundation also has been recognized for its OutGiving program, through which the foundation seeks to build a larger base of philanthropists giving strategically in support of LGBT causes. In recognition of the OutGiving program, Liberty Hill Foundation honored Tim Gill with its Upton Sinclair Award in 2011 "for his vision, passion and leadership in helping to create and continuing to inspire the modern day LGBTQ donor movement."
The Gill Foundation invests a significant portion of its funding in its home state of Colorado, supporting nonprofits working to improve the quality of life for all Colorado residents. In 2016, $1.7 million was invested in Colorado organizations. The foundation is particularly well known in Colorado for its Gay & Lesbian Fund for Colorado program. The Gay & Lesbian Fund's $1 million challenge grant in 2005 to the Mile High chapter of American Red Cross was one of the largest non-corporate donations in the country for Hurricane Katrina disaster relief.
At its inception, the Gill Foundation office was based in Colorado Springs. In June 2012, to consolidate operations, the Gill Foundation closed down the office in Colorado Springs while continuing its presence in Denver. The foundation donated the Colorado Springs building to Rocky Mountain PBS to create the Tim Gill Center for Public Media.The foundation reevaluated the future direction of the Gay & Lesbian Fund, although it remains committed to its Colorado programs.
- Brad Clark, President & CEO
- Penny Hamilton, Chief Operating Officer
- Heidi Overbeck, Vice President of Communications
- Karen Wick, Vice President of Programs
- Jeff Criteser, Director of OutGiving
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- "Caroline Preston". Grant Making to Gay Causes Exceeds $750-Million. Retrieved 22 Feb 2012.
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- "Allison McGee Johnson". Foundation Management: Getting the Most Out of Giving. Retrieved June 2004. Check date values in:
- Ustinova, Anastasia (March 31, 2008). "Philanthropists ensure gay community's future". San Francisco Chronicle. Retrieved 11 November 2015.
- "Tim Gill to Receive Liberty Hill Foundation's Highest Honor". PR Web. Retrieved 11 November 2015.
- "Gill Foundation 2016 Annual Report".
- "Coloradans Can Get Red Cross Donations Matched". ABC 7. September 2, 2005. Retrieved 11 November 2015.
- "Karen Auge". Gill Foundation to re-evaluate Gay & Lesbian Fund's grant-giving. Retrieved 14 Oct 2011.
- Official website
- Meet the Megadonor Behind the LGBTQ Rights Movement
- The Advocate Op-ed: Where will activism dollars go next?, Feb. 3, 2014
- Johnson, Dirk (11 December 2007). "Grants for Gay Services Grow and Go Mainstream". The New York Times. ISSN 0362-4331. Retrieved April 12, 2012.