My wife and I found a neat little handbook 60 pages long published in 1927 by the US DOI. It lists the then 19 National Parks. Here are some highlights:
Hot Springs NP in Arkansas predates Yellowstone, created in 1832 (Yellowstone in 1872). I always thought Yellowstopne was the first NP created; maybe Hot Springs was designated something else then absorbed into the system later on? Were they even thinking of National Parks in 1832?
(Related to other points in this thread, seems Hot Springs, at 1.5 sq miles, should go the way of Sullys and Platt, sort of an anachronism these days and nothing more)
Hawaii National Park is listed as one NP, including the volcanoes of Mauna Loa, Kea and Haleakala.
Its listings of National Monuments includes Casa Grande - no mention of it as a NP earlier than 1927. Many listed later became NP. Many still exist as NMs, and some seemed to have simply disppeared, absorbed into some other unit, such as Fossil Cycad NM in South Dakota, Olk Kassan in AK, Verendrye in ND...