Thayer is one hard name to dig up information on. In researching the name I've found many different sources listing many different origins. In French, Thayer is pronounced tie-YHER, supposedly meaning "army of the nation." One source suggests it is an Old English phrase meaning "the people," from origins elsewhere. Other ties lead to Germany, where there were several bearers of the name, though there were others in Austria, and the meaning is listed as "wild animal." There is a strong possibility it comes from the French word for "tea cup,"théière," possibly in reference to those who made them. It could be an Old English name that is possibly related to the occupational surnames Taylor or Thatcher, both of which are currently popular as first names. The name Thatcher means "roof thatcher" in Old English and was worn by former British Prime Minister Margaret Thatcher. I recall the name from when I was very young, reading a book called Jeremy Thatcher the Dragon Hatcher. However, it is more likely Thayer comes from Taylor, as opposed to Thatcher, as a regional dialect or French variant. Taylor ("tailor") ranked at #44 in 2011 for girls, and #337 for boys. My favorite explanation, and the one that sounds most reasonable and accurate, is French, "tea cup maker."
Occupational surnames are unique in that they do work for both genders, unlike strictly masculine surnames such as Anderson, meaning "son of Anders/Andrew," and, unfortunately for adventurous namers, girls cannot be born sons. On a happier note, roof thatchers, tailors, brick layers and more can be men or women nowadays, which is why I'll be listing Thayer as unisex. For strictly feminine surnames, look to Scandinavian surnames such as Leifsdottir, meaning "daughter of Leif." I dare say it might be strange to give surnames such as these anywhere but America, though. I don't think you'd find any Leifsdottir Sorensdottir's or Thayer Anderson's elsewhere.
Some of the first Thayer's (as a surname) to come to America settled down in Braintree, Massachusetts, where you can still find Thayer Academy. Thayer featured as a character in F. Scott Fitzgerald's novel This Side of Paradise. It was the first name of a character on the TV show "The Lying Game," and the likelihood of that character's name being given due to Mount Thayer in California is strong. Thayer is a place name in several U.S. cities. In 2011 there were only 20 baby boys named Thayer.