How many slaves did Lewis and Clark have?

On the expedition, there was one slave that accompanied them. His name was York, and he was Clark's slave, willed to him by his father. But Clark did not like to refer to him as slave, so in the journals he just called him "my servant". The two men had grown up together. York was tall, strong, a valuable member of the expedition, and devoted to Clark, who freed him when they returned to St. Louis. Subsequently Clark set him up in the draying business.