ELI5 How Did The Economy Sustain Itself When 90% of People Were Farmers?

I was reading this article PBS that said in 1862 90% of Americans were farmers. How did an economy sustain itself when this many people were farmers? The Census taken in 1860 said that were 31,443,321 Americans. So about 28.2 million of them were farmers? How could that many people sell food and other agricultural products for a living?