 The addition of "Primo" (Italian for "first") to Casorate came about on March 15, 1863, due to it belonging to what was at the time the First District of Milan, and it has since then been named thus.The origins of Casorate Primo are not clearly known.The first evidence of settlement in the current location of the town date back to the 2nd and 3rd centuries AD, during the ancient Roman dominion of the area (at which time the land was part of Cisalpine Gaul, due to being inhabited by Celtic peoples, such as the Insubres).