If you are living in the US either as a US Citizen, a Legal Permanent Resident (LRP) or in any other non-immigrant capacity (such as someone on a student visa) and you require a UK visa, you will most likely need to submit your application for UK Visa in USA.

There are some occasions or situations where you cannot submit your  application for UK Visa in USA. For example, when making your application for UK Visa in USA you will need to evidence your residency in the US , otherwise the UK Immigration office may not accept your application.

Why you may not be able to make your application for UK visa in the USA even though you currently live in the US:

What can you do to convince the UK Immigration to accept your application for UK visa in the USA

Why would someone who has no legal reside to reside in the US want to make application for UK visa in the USA .

There are many reasons why a person my need to travel to the UK even though they have not resolved their legal residency in the US. Many times, the situation warrants that they make application for UK visa in the USA .

There are many more examples that we can think of, what is most important is to employ the services of a UK immigration lawyer if you find yourself in any of these situations