At its greatest extent, the U&D extended 107 miles (172 km) from Kingston Point on the Hudson River through the Catskill Mountains to its western terminus at Oneonta, passing through the counties of Ulster, Delaware, Schoharie and Otsego.

Although Cornell made plenty of money from shipping, he planned a railroad that would bring supplies from towns in central or western New York to his port in Rondout.

It would go from Rondout to the busy city of Oneonta on the upper Susquehanna River, and then to Oswego on the shore of Lake Ontario.

The R&O at 12 miles (19 km) long reached the summer vacation resort of Olive Branch, near the town of Shokan, on September 30, 1869.

[4] The same year, ownership of the railroad was transferred to John C. Brodhead [5] and the line reached the small town of Big Indian.

Much of the freight income was made from coal shipped along the D&H Canal from the Moosic Mountains near Carbondale, Pennsylvania, to the port at Rondout.

This increased service provided the first real rail route into the Catskill Mountains, benefiting both passenger and freight customers.

Another boon to business was a ferry that ran across the Hudson to Rondout from Rhinecliff, with a Rhinebeck and Connecticut Railroad and New York Central and Hudson River Railroad station (the current Amtrak station), connecting the cities of Hartford, Connecticut, Providence, Rhode Island and Boston, Massachusetts to the region.

The town (and later city) of Kingston, New York (centrally located on the Hudson River) was profitable to the railroad, due to the large number of industries of the area, including cement, concrete, bricks and bluestone.

Kingston was also a popular passenger stop, as people would rely on the railroad to take them around the Catskills to jobs at mills and small factories.

[4] Cornell got the idea for another railroad that would start at the U&D junction in Phoenicia and go up along the Stony Clove Valley to the bustling village of Hunter.

Industries on this line included the William O. Schwartzwalder Furniture Factory, in the company-owned hamlet of Chichester.

By the time of the Great Depression of 1929 and thereafter, most of the passenger traffic had been lost to private cars on improved highways, buses and shared limousines (called "hacks"); trucks had taken most of the non-commodity freight business; and the railroad was in serious financial trouble and a shadow of its former self.

The New York Central acquired the failing U&D on February 1, 1932, under pressure from the Interstate Commerce Commission (see "Ulster and Delaware: Railroad Through The Catskills", by Gerald M. Best).