Key lime pie is closely tied to Key West. The filling that defines it — lime juice, sweetened condensed milk, and eggs — made sense in a place that had limes and canned milk long before reliable refrigeration and local fresh milk.
Sweetened condensed milk matters to the story. Gail Borden’s process for preserving milk with sugar dates to the 1850s, and the canned milk traveled by ship and later by train. In the Keys, that can was far more practical than fresh cow’s milk. That is why a classic key lime filling is built on condensed milk rather than cream or fresh milk.
Local residents of Key West have long been called Conchs. The traditional account is that cooks there made a lime pie with what they had: canned milk, eggs, and the small local limes. One often-repeated story credits a cook known as Aunt Sally in the household of William Curry, a 19th-century Key West figure. That story is part of local lore; it is not something we can pin to a dated, contemporaneous recipe in this guide.
What can be documented
Keys researchers have pointed to “lime pie” on a Key West restaurant menu published in the Key West Citizen on January 27, 1926 (the Green Lantern, at 10 cents). In 1939, the Miami Herald printed a “Lime Pie” recipe from Mrs. L.E. Blackwell that used egg yolks, lime juice, condensed milk, a baked pastry shell, and a meringue, and that said the recipe had been used in a Key West family for more than half a century. Those items are real published evidence that a condensed-milk lime pie was already at home in the Keys.
Food writer Stella Parks, in her book BraveTart, argued that the no-bake condensed-milk formula tracks a 1931 Borden “magic lemon cream pie” recipe used to sell canned milk, and that clear printed Florida recipes for the no-cook version are hard to find before that date. Key West writers have pushed back, citing the menu and family recipes above. This site does not pretend the argument is settled. The honest summary is: the pie is a Keys dessert in tradition and in early local evidence, and the exact birthday of the no-bake formula is still debated.
Crust, cooking, and toppings
Older written recipes often use a pastry crust. The graham-cracker crust is the version most people bake at home now. Some traditional pies were not baked — the lime juice was credited with thickening the yolks — while others, including the 1939 Blackwell recipe, went into the oven and were finished with meringue. Recipes from the mid-20th century already show pies with no topping, with whipped cream, and with meringue. Our classic recipe uses a graham crust and a short bake, which is also the safer way to handle a filling made with eggs.
National Key Lime Pie Day is observed on September 26. The date shows up on popular food-day calendars (it was circulating on food blogs and social media by 2015). It is a calendar observance, not a federal holiday, and you do not have to wait for it to make the pie.