Complex sentence: In 1859, it was renamed for Sir Joseph Paxton, architect of the Crystal Palace, who was a major shareholder in the Illinois Central Railroad, which in 1856 was the longest span of railroad in the world (Chicago to Cairo).
Split into simpler sentences: In 1859, it was renamed for Sir Joseph Paxton, architect of the Crystal Palace, who was a major shareholder in the Illinois Central Railroad. In 1856, the Illinois Central was noted as the longest span of railroad in the world (Chicago to Cairo).