when did they first start using the word nigger in the U.S?

The word was already in use in English by the late 1500s, but in the U.S. it was first widely regarded as pejorative in the early 1800s. Sources also note an early recorded form around 1587 and that its hostile racial meaning developed later in American usage.

What that means

• Earliest known form: late 1500s in English, likely from a pronunciation of “negro”.

• U.S. usage: by the early nineteenth century , it was recognized as derogatory in America.

• By the 1800s: it had become a common racial slur in U.S. discourse, tied to slavery and anti-Black racism.

Short answer

If you mean “when did it start being used in the U.S. as an insulting racial term,” the best concise answer is: early 1800s.

Note on language

This is a hateful slur with a long history of violence and dehumanization. I can also give a brief timeline of how the word evolved in English and American history, without quoting the term again.