What chemical element is also a state of the United States?

Californium

https://en.wikipedia.org/wiki/Californium

Californium - the atomic number is 98 and the chemical symbol is Cf. The name derives from the state and the university of California, where the element was first synthesized.

Here is a nice list of Chemical Elements named after places...

https://en.wikipedia.org/wiki/Chemical_elements_named_after_places

Al Alabama, Aluminium
Co Colorado, Cobalt
Ca California, Calcium
Ne Nebraska, Neon
Ga Georgia, Gallium
La Louisiana, Lanthanum
Md Maryland, Mendelevium
Ar Arkansas, Argon
Mo Missouri, Molybdenum
Nd North Dakota, Neodynium
Pa Pennsylvania, Protactitinium
Nh New Hampshire, Nihonium
Mt Montana, Mietnerium
Mn Minnesota, Manganese
Fl Florida, Flerovium
Sc South Carolina, Scandium
In Indiana, Indium

https://www.sporcle.com/games/javiern/states-and-chemical-elements