In can always be used to describe location in a country: in India, in the United States, in Japan. In is also used with cities: in Delhi, in Washington, in Tokyo, but in some contexts, at may also be found. It has long been the practice, for example, to speak of ‘Her Majesty’s Ambassador at [name of capital]’. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.