I set myself a life-long goal a few months ago to visit every National Park and Monument in the United States. The way I'm counting there are currently 61 National Parks and 131 National Monuments (March 2019). This number changes occasionally, for instance when I started this goal there were 59 National Parks but in February 2018 Jefferson National Expansion Memorial was renamed to Gateway Arch National Park and in February 2019 Indiana Dunes National Lakeshore was designated as a National Park, so they made the list. All National Parks are managed by the National Park Service and National Monuments may be managed by a number of different agencies. So this list really depends more on the name of the place than what it actually is, but I needed to draw the line somewhere and they do all have some form of historical, cultural, or environmental significance.
As of now (March 2019) I have visited 17 National Parks and 19 National Monuments. Below is the list of the ones I have been to in the order that I have visited them with links to associated blog posts (if I made them yet).
NATIONAL PARKS
Great Smoky Mountains - August 2011
Olympic - January 2017, January 2019
Grand Canyon - March 2017, March 2018
Zion - March 2017
Badlands - June 2017
Yellowstone - June 2017, October 2018
Grand Teton - June 2017, October 2018
Glacier - June 2017
Crater Lake - June 2017
Redwood - June 2017
Yosemite - June 2017
Rocky Mountain - June 2017
Acadia - October 2017, October 2018
Petrified Forest - March 2018
Mesa Verde - March 2018
Arches - October 2018
Mount Rainier - January 2019
NATIONAL MONUMENTS
Statue of Liberty - 2000
Grand Staircase-Escalante - March 2017, March 2018
Devil's Tower - June 2017
Capulin Volcano - June 2017
White Sands - June 2017, March 2018
El Malpais - March 2018
El Morro - March 2018
Montezuma Castle - March 2018
Tuzigoot - March 2018
Walnut Canyon - March 2018
Sunset Crater Volcano - March 2018
Wupatki - March 2018
Canyon de Chelly - March 2018
Hovenweep - March 2018
Canyons of the Ancients - March 2018
Chimney Rock - March 2018
Petroglyph - March 2018
Colorado - October 2018
Mount St. Helens - January 2019