When Lincoln referred to four scores and seven years ago what year was he talking about?

When Abraham Lincoln referred to "four score and seven years ago" in his Gettysburg Address, he was talking about 1776, which is 87 years prior to the speech delivered in 1863. A "score" is 20 years, so four score equals 80 years, plus seven years makes a total of 87 years. Thus, he was referencing the founding of the United States and the signing of the Declaration of Independence.