Mt. Rainier, 1896
I've finished the brief history of the boundary of Mt. Rainier NP, see descritption and map. As you can see from the map the original NP was considerably smaller in size, thought to have been square but wasn't due to kinks in the township and range land plat system in use. That was resolved with the 1931 law adding new lands to the NP.
Subsequent changes occurred in 1988 and 2003, but these were mostly smalll additions or inclusions of land for better management of the NP resources, and with one small removal for Crystal Mountain ski resort's ski operations. The 1988 was for inclusion of adjacent USFS land for the NP to completely encompass the Stevens Canyon Road (southeast) and Westside Road (west central) into the NP and NPS management.
The 2003 was the inclusion of land just outside the northwest corner, the Carbon River entrance, for space for visitor facilities (parking, camping, building, etc.) because the land inside the NP was susceptible to flooding, namely 2006 and 2008 which destroyed number NP facilities, and the NP has approved the new Carbon River plan to move all but essential services to this new land, to close the old road, which has been temporarily closed since 2006, and to reroute the trail.
This addition will probably be the last in some time since it took so long to negotiate swapping private timber lands, and expensive. There still is a need to add land to the NP, but much of the land is in the USFS lands and has been logged. But that said, there is land in the northwest and southwest corner, the river corridors, which would benefit the NP for better management.
Anyway, that's the latest update. More is on the way over the next few weeks.