When most people hear the word nonprofit, public charities such as the American Red Cross and Big Brothers Big Sisters of America are the first types of organizations that come to mind.

More than 1.5 million nonprofits were registered with the IRS as tax exempt as of September 12, 2016. Although two-thirds of organizations within this pool are indeed public charities, there are also many organizations whose nonprofit status routinely surprises the journalists, researchers, and everyday users who discover their GuideStar Nonprofit Profiles.

We thought it'd be fun to share these Four Famous Organizations You Might Not Know Are Nonprofits. Who on this list surprises you?

1. New requirement for organizations intending to operate under Section 501(c)(4): Submit Form 8976

New legislation enacted at the end of 2015 added section 506 to the Internal Revenue Code. Section 506 requires an organization to notify the IRS of its intent to operate as a section 501(c)(4) organization.