In general, the MLA follows The Chicago Manual of Style for the capitalization of academic department names (“Academic Subjects”) and administrative bodies (“Administrative Bodies”).

We capitalize the official names of academic departments (e.g., Department of Comparative Literature), but we do not capitalize the adjective forms of such departments (e.g., the comparative literature department). In the adjective forms, we do capitalize the name of the academic subject if it is a proper noun (e.g., the English department).

We also capitalize the names of most administrative bodies (e.g., Department of State, the State Department). 

When you are styling department names, we recommend that you strive for consistency and keep a style sheet that lists any exceptions.

Works Cited

“Academic Subjects.” The Chicago Manual of Style, 17th ed., sec. 8.85, U of Chicago P, 2017, www.chicagomanualofstyle.org/book/ed17/part2/ch08/
psec085.html.

“Administrative Bodies.” The Chicago Manual of Style, 17th ed., sec. 8.63, U of Chicago P, 2017,  www.chicagomanualofstyle.org/book/ed17/part2/ch08/
psec063.html