Yes, I would assume so...I wonder what decade had the most car makers...the 1910s or 1920s I assume. By 1940 there weren't many independents left.
I believe the first quarter of the 20th Century, 1900-1925. That was still the era of almost unbridled entrepreneurship in this country, and virtually every town or city of any size had its share of blacksmith shops, even machine shops--a blending of which was all that was necessary (along with some $$ of course) to set up a factory to build automobiles.
Most makes of cars back then (well beyond the already establishing major companies) were in a sense, makers of what became called "assembled" cars--meaning that they outsourced at least certain major components, principally engines and transmissions, and as things progressed, body shells (GM, for example, produced none of their own bodies until the Fisher Brothers (name became Fisher Body Division in the middle 1920's, with Lawrence P. Fisher having been President and later Chairman of GM back then) merged into GM. Chrysler Corporation built none of their own bodies until the buyout of Briggs Body Company in 1954. Ford outsourced most of their closed body styles well into the Model A and early V8 years as well.
But, in a very real way, those early years were still the era of "Build a better mousetrap, and the World will beat a path to your door!" thinking. Couple that with the simple fact that not until the middle 1920's did there exist a true integrated network of Federal highways, even some states in the Midwest and West not even having state highway routes until then. That meant there was virtually no intercity nor interstate truck transportation readily available, and railroad shipment of built cars was somewhat erratic and certainly expensive (Ford could only ship perhaps 4 Model T's in the then standard 36' wooden RR boxcars of the day!).
So, it's little wonder that in so many small cities, even a few rather small towns, that some enterprising person would decide that his future rested on being the next automobile manufacturer.
Of course, the vast majority of US automakers did not survive--many of them lasted no more than 4-5 years, some failing after fewer than a dozen cars. And of course, today, of all those startup automakers, the cars they made simply do not exist, or if they do, it's a rusty chassis here, a few vestiges of a body shell there, or an obscure engine laying around--their marques long forgotten in the dustbin of history. And yet, for some of them, a pristine example still exists, in a museum someplace.