As Eva Luna says, it depends where you are. Here is a PDF map of the US, shaded by percentage of India-born immigrants in each county. It is clear that the two highest concentrations are in the New York metro area and the San Francisco Bay Area (especially in Silicon Valley, about 50km to the southeast of San Francisco). Note that these are percentages not absolute populations: Chicago and Los Angeles may have more India-born immigrants than the Bay Area, but they’re not as high a percentage. In the Bay Area especially, it’s largely due to the prevalence of India-born engineers. This demographic is generally well-educated, sophisticated, and affluent. Hence, there’s a huge number of Indian restaurants around here, ranging from low-cost “buffet lunch” places to upscale “destination” restaurants. As I mentioned in post #46 above, there are more than 12 Indian restaurants (I think it’s 14, but one may have closed recently) in my Silicon Valley city of 70,000 people. I can easily walk to 10 of these. Around these parts, the word “Indian” invariably refers to people from the South Asian subcontinent.
On the other hand, in most parts of the US, India-born immigrants are much rarer (and most people’s first thought on hearing “Indian” would be “Native American”). I’d be willing to bet – but can’t support with evidence – that the majority of US residents nationwide have never eaten “Indian food” (although as an aside, might that not also be true of residents of France, taken as a whole?). Compare that with Chinese food: even small US towns that have little or no Chinese immigrant populations will have a “Chinese Restaurant” (whether or not it serves anything that bears resemblance to real Chinese food, or is run by anyone with any Chinese ancestry). So, I’d say that most Americans have eaten “Chinese” but a minority have eaten “Indian”.
Apart from the Indian engineers to be found in any high-tech area (Silicon Valley, Silicon Forest, Silicon Prairie, Boston’s Route 128), the other “stereotypical” Indian occupations in the US are family-owned small businesses such as convenience stores (think Apu on The Simpsons) and hotels / motels. These are both business models where hard work and strong family ties can pay off with little risk of the initial investment, and multiple generations can participate. However, the familial nature of both of these business models, stressing meals at home (especially if there’s a store or motel to be looked after during the meal), tends not to support large concentrations of Indian restaurants in the same way that a population of young, single, disposable-income-rich, workaholic Indian engineers does.
The US is a huge country, and different areas have attracted different immigrant groups. Here in Silicon Valley, the local buses and light-rail trains have signs in English, Spanish, and Vietnamese (San Jose has a large Vietnamese population, which might not be obvious at first glance). A few miles from me is Fremont, the city with the largest Afghan population in the US (part of it is known as “Little Kabul”). One block from Little Kabul is the Naz 8 cinema multiplex, specializing in films from “India, Pakistan, Afghanistan, China, Taiwan, Korea and Philippines”.
Pick 100 US residents at random, and you’ll get 100 different experiences with Indian food (compared to the UK, where everyone knows what Chicken Tikka Masala is). I’d still claim that most of the 100 would never have tasted it, or perhaps even laid eyes on an Indian restaurant. Most Americans don’t have a friend or acquaintance from India (although, if you took the Indians out of Silicon Valley, the high-tech machine would wither overnight!). One can drive thousands of miles in the US without finding a curry[sup]*[/sup], whereas “American Chinese” exists in virtually every small town and each suburban mall’s “food court”.
[[sup]*[/sup]My personal “Earthquake Supply” shelf is heavily stockpiled with prepared Indian meals in ready-to-cook pouches: whatever perils the Apocalypse may bring, it’s no excuse to eat bland food! 
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And, look what I found: £