MacArthur Foundation — Website: https://www.macfound.org/

Note: The Wikidata source explicitly lists 'official website https://www.macfound.org/' in the structured data for the MacArthur Foundation (Q1424691). The claimed URL matches exactly with the source data, with only minor formatting differences (the claim includes 'https://www.' while the source lists 'https://www.macfound.org/', but these refer to the same website). The source also references this URL multiple times in citations (e.g., 'https://www.macfound.org/about/our-history/' and 'https://www.macfound.org/social'), further confirming it as the official website.