Records exist for all 50 states, and for the contiguous 48 states (i.e., excluding Alaska & Hawaii).
Whit Rambach provided the following progression of the FKT for 50 states. We have not researched these to find more information.
07-19-2018 Colin O'Brady - 21d 9h 47m
08-07-2016 Maddie Miller - 41d 16h 10m (FEMALE)
07-16-2010 Mike Moniz, Matt Moniz - 43d 3h 51m
07-25-2008 Mike Haugen, Zach Price - 45d 19h 2m
08-07-1994 Whit Rambach, Todd Huston - 66d 21h 47m
07-12-1990 Adrian Crane - 101d
Also, to date (Dec. 2019) three people have completed all 50 states highpoints TWICE, with the FKT (and first completion) being Whit Rambach in 5 years 91 days, completed 8/31/1999.
Progression of this record for the contiguous 48:
30 days - Dennis Steward and the "Highpoint Hoppers" (1991)
23 days, 19 hours, 31 minutes - Jake Meyer (2006)
19 days, 7 hours, 17 minutes - Josh & Lindsay Sanders (2015)
We should probably have Colin O'Brady's "50 high points" record up here too
"In the summer of 2018, Colin took on the 50 US High Points. After a 13,000 mile journey in 21 days, 9 hours, and 48 minutes he completed the 50 high points challenge, setting a new world record. In the last 7 days of the project alone, in an astonishing final push, Colin climbed the 7 highest peaks in the lower 48 US states, totalling over 100 trail miles and over 50,000 feet of elevation gain. Along the way, Colin invited others to join him at their state’s high point and be part of what he called the “Forest Gump effect”."
Unsure of his time for the 48 though