Before meatloaf became popular, a common American dish is "meat porcupine" or "porcupine meatball" where minced meat is mixed with breadcrumbs and eggs and shaped into a porcupine and various edible "quills" are added to the surface. There is a book from 1769 called The Experienced English Housekeeper and it included this dish.

Jean Anderson's American Century Cookbook: The Most Popular Recipes of the 20th Century says:

"Was meat loaf too homely a recipe to make American cookbooks published in the nineteenth century or earlier?...I find no meat loaves in American cookbooks before the 1880s; these were primarily veal loaves (a more economical meat early on than beef) and altogether different from the meal loaves so familiar today...Sarah Tyson Rorer offers a slightly more elaborate veal loaf in Mrs. Rorer's Philadelphia Cook Book [1886] along with something called "Cannelon," which is clearly the precursor of meat loaf as we know it today...Cannelons appear in cookbooks right into the 1920s, although by this time meat loaves were outnumbering them. Were meat loaves slow to come because of the lack of meat grinders? Or was it because of unreliable refrigeration (ground raw meat is extremely perishable)? Possibly a bit of both, but I can't say for sure... Though simple loaves of chopped meat may have been made during America's infancy and adolescence, only in the twentieth century did meat loaves truly arrive. And, yes, many of them did come out of big food company test kitchens. Like it or not."