Does a UK degree have the same classification in the US? Does a degree obtained in the UK have the same classification in the USA? So if I had a 2:1 in England would it be a 2:1 in the USA or something different?
The honors degree classifications that exist in the UK (described in this question and its answers) don't exist in the US. In the US, instead of earning a degree of a certain "class," students (usually) earn a GPA on a scale of up to 4.0 points, and that number is used to indicate their performance.

"Honors" like  summa cum laude and magna cum laude exist, but not at all universities, and don't have a standard meaning across universities (or even across departments in the same university). They aren't used in the same way that UK degree classifications are. For example, you won't find an application for graduate studies that specifies that applicants should have graduated magna cum laude  - instead, they may specify a minimum undergraduate GPA.