The following content is from History.com:
In addition to the United States, Valentine’s Day is celebrated in Canada, Mexico, the United Kingdom, France and Australia. In Great Britain, Valentine’s Day began to be popularly celebrated around the 17th century.
By the middle of the 18th, it was common for friends and lovers of all social classes to exchange small tokens of affection or handwritten notes, and by 1900 printed cards began to replace written letters due to improvements in printing technology. Ready-made cards were an easy way for people to express their emotions in a time when direct expression of one’s feelings was discouraged. Cheaper postage rates also contributed to an increase in the popularity of sending Valentine’s Day greetings.
Americans probably began exchanging hand-made valentines in the early 1700s. In the 1840s, Esther A. Howland began selling the first mass-produced valentines in America. Howland, known as the “Mother of the Valentine,” made elaborate creations with real lace, ribbons and colorful pictures known as “scrap.” Today, according to the Greeting Card Association, an estimated 145 million Valentine’s Day cards are sent each year, making Valentine’s Day the second largest card-sending holiday of the year (more cards are sent at Christmas). Women purchase approximately 85 percent of all valentines.