In 1800 the French ruler Napolean Bonaparte signed the Treaty of San Ildefonso with the Spanish King.

The Treaty of San Ildefonso, signed in 1800, transferred ownership of Louisiana from Spain to France. This later facilitated the United States' acquisition of the Louisiana Territory through the Louisiana Purchase in 1803.

The Treaty of San Ildefonso was signed in 1800, between France and Spain, secretly agreeing to transfer Louisiana from Spain back to France. This paved the way for the eventual sale of the Louisiana Territory to the United States in the Louisiana Purchase of 1803.

The population of San Ildefonso is 5,702.

Spain returned the colony of Louisiana to France.