There has been a scholarly interest in the demographic characteristics of American environmental organizations since the 1960s, but until recently there was no readily available way of knowing the composition of the staff or board of these institutions as few revealed any of their demographic data publicly. For the past five years, there has been a high-profile campaign to get environmental nonprofits to disclose their demographic data. This paper examines 12,054 small, medium-sized, and large environmental organizations to find out how many of them have released diversity data on GuideStar. The article also examines how the state in which organizations are located, region of the country, urban or rural setting, organizational typology, amount of revenue, size of the staff, size of the board, gender of the chief executive officer (CEO), race of the CEO, and the year of completion of the GuideStar profile influenced the disclosure of diversity data. The researchers collected financial data from Internal Revenue Service tax forms and diversity data from GuideStar. The study found that 3.7% of the nonprofits studied divulged diversity data. However, organizations in the Pacific and Mid-Atlantic regions were most likely and nonprofits in the South least likely to report diversity data. Urban nonprofits were more likely to divulge diversity data than those located in the suburbs or in the rural areas. The highest level of reporting was in Washington, D.C. In addition, environmental justice organizations were more likely to disclose diversity data than other types of organizations. The larger the staff and the higher the revenue, the more likely it is that the organization divulged its diversity data. Organizations with female CEOs were more likely to reveal diversity data than male-headed nonprofits. Environmental organizations with ethnic/racial minority CEOs were also more likely to disclose demographic data than organizations with white CEOs.