The Hill is Home’s own Maria Helena Carey was recently asked by Washingtonian magazine the eternal question: Does one live ‘on Capitol Hill’ or ‘in Capitol Hill’? While you’ll have to seek out a paper copy of the magazine to read her full answer, I can say here that Carey quite correctly pointed out that the preposition to use is ‘on,’ and that got me to thinking about how often each of these formulations is used. (We will be sure to post a link if they ever put that article on line)
I started my research at Google Ngram, which charts how often certain words or phrases are used in books published between 1800 and 2019 (See, for instance, how the word “theater” in American English did not begin to be used until about 1840, and then slowly began taking over from “theatre” until reaching parity in 1940, then pulling away starting in the early 1970s)
As far as Ngram is concerned, the phrase “in Capitol Hill” does not exist, it is all “on Capitol Hill.” A quick search on Google Books confirms this: There are plenty of instances of “on Capitol Hill,” including a number of books that use it in their title – probably most famously Margaret Truman’s “Murder on Capitol Hill.”
In contrast to Ngram, a search through Google books directly does find a number of hits for “in Capitol Hill.” However, there are well over a million hits for “on,” and only about 10,000 for “in.” It should also be noted that there are lots of other Capitol Hills, most famously in Seattle, but also Oklahoma City, Salt Lake City, Montgomery, and Denver – and that there, “in” seems to be the preferred preposition.
Looking through another of my favorite databases, I found that “on” clocks in at over 2400 hits at Chronicling America, which boasts over 20 million newspaper pages published between 1770 and 1963, the first time in 1842. The phrase “in Capitol Hill” only appears about 120 times in that same stretch, and while most of the former are real uses of the phrase, the latter hits seem almost entirely false positives (a list of locations a movie theaters a certain film is playing lists a “drive in” before a “Capitol Hill” theater, for instance)
Similarly, the HathiTrust collection of some 18 million books has the phrase “on Capitol Hill” in over 150,000 books, while “in Capitol Hill” appears in fewer than 4,000 – and, again, a large number of the latter refer to Capitol Hills far from Washington D.C.
In short, it is not just correct to use “on” with “Capitol Hill” when referring to our neighborhood but also what is and was most used in print. Now, as to why this would be – after all, I don’t think that anybody would say they lived “on Capitol Heights” – that is a question for the linguists out there.