Thanks to the movies and mid-20th century TV, when we think of men’s underwear in the Old West, we usually picture the union suit, a garment that looked like a cross between a onesie and today’s longjohns, with buttons up the front and a flap in the back to accommodate nature’s needs. But union suits weren’t always a single piece — it was possible to buy shirts and pants separately. They also came in an above-the-knee length (for the especially hardy).
Less well-known were garments called “linens”, from the material they were made out of. Linens could be long, though they were usually knee-length or shorter. They had buttons or grommets with laces, and some had wide waistbands. Even more obscure was a cotton garment with buttons and ribbed legs that’s quite similar to the recently-popularized “boxer-briefs”. From my research, I believe these were among the first to be considered “drawers”.