In several places in Mark Twain and C.D. Warner’s novel The Gilded Age, the word “deepo” is used.
One such occurrence is the following:
Dilworthy will be elected to-day, and by day, after to-morrow night he will be in New York ready to put in his shovel—and you haven’t lived in Washington all this time not to know that the people who walk right by a Senator whose term is up without hardly seeing him will be down at the deepo to say ‘Welcome back and God bless you; Senator, I’m glad to see you, sir!’ when he comes along back re-elected, you know.
Is this an old way of spelling “depot,” or what is the story here?
‘Deepo’ is not so much an “old way” of spelling ‘depot’ as a way of spelling it typical of a variety of 19th century Southern humor. That variety of humor featured ersatz phonetic spellings in imitation of dialectical and vernacular pronunciations, or at least spellings intended to evoke a sense of such pronunciations by the fictional speaker.
For example, George William Bagby (aka Mozis Addums) in an 1867 publication, uses it thus:
The Native Virginian (Orange, Virginia), 15 Nov 1867, p 2 (paywalled link).
Other examples, although a bit thin on the ground, appear in similar contexts in the popular press in the years prior to the 1873 publication of The Gilded Age. The contexts make clear that ‘depot’ is the intended word.