The U.S. Post Office and U.S. Army and Navy officials, in conjunction with the American advertising and greeting card industries, threw a Christmas in July luncheon in New York in 1944 to promote an early Christmas mailing campaign for service men overseas during World War II.[9] The luncheon was repeated in 1945.[10]
The future of Christmas in July
American advertisers began using Christmas in July themes in print for summertime sales as early as 1950.[11] In the United States, it is more often used as a marketing tool than an actual holiday. Television stations may choose to re-run Christmas specials, and many stores have Christmas in July sales. Some individuals choose to celebrate Christmas in July themselves, typically as an intentionally transparent excuse to have a party. This is in part because most bargainers tend to sell Christmas goods around July to make room for next year's inventory.[12]
https://en.wikipedia.org/wiki/Christmas_in_July