Cedar Hill Yard is a classification yard located in New Haven, North Haven and Hamden, Connecticut, United States. It was built by the New York, New Haven and Hartford Railroad (often known simply as The New Haven) in the early 1890s in and around New Haven's Cedar Hill neighborhood, which gave the yard its name. Electrical catenary for electric locomotives was added to the yard in 1915. To handle increasing traffic as a result of World War I, the yard was greatly expanded between 1917 and 1920 with additional construction along both sides of the Quinnipiac River. The construction project added two humps where railroad cars were sorted into trains by gravity. The yard was further modernized in the 1920s, becoming one of the busiest railroad yards in the United States, and the most important yard in the entire New Haven Railroad system.

At its peak during World War II, Cedar Hill Yard handled more than 5,000 railroad cars per day. Following the end of the war the yard's importance began to decline, as freight traffic across New England shifted to road transport, and heavy industry left the region. Much of the yard began to fall into decay following the New Haven Railroad's bankruptcy in 1961. Following the opening of the newly rebuilt Selkirk Yard near Albany, New York, in 1968, much of the traffic formerly handled at Cedar Hill Yard was directed there instead, and car float service between Cedar Hill Yard and New York City ended.

In 1969, the Penn Central Transportation Company took over the yard as part of its purchase of the New Haven Railroad. The yard's new owner promptly removed the electrical catenary and shut down one of the yard's two humps to save money. The next year, Penn Central went bankrupt, and the yard continued to deteriorate from deferred maintenance. Under Penn Central, the yard's importance further declined when the Poughkeepsie Bridge, the yard's key link to the rest of the United States, was damaged by a fire in 1974 and not replaced. Conrail, a new freight railroad formed by the United States government to reverse the fortunes of Penn Central and other bankrupt Northeastern United States railroads, took over operations in 1976. The yard's new owner initially made some improvements, but in 1980 decided to close the yard's remaining hump and move more operations to the yard in Selkirk. Cedar Hill Yard continued to be used to classify freight trains, but was turned into a flat yard, with trains built up and broken down by switcher locomotives.

Cedar Hill Yard was operated by Conrail until 1999, when CSX Transportation purchased Conrail's New England operations. In the first decade of the 2000s, CSX expanded the yard's operations by constructing a bulk cargo transfer facility, where bulk commodities are transferred between trains and trucks. CSX was joined in the yard by other railroads, including Amtrak, which uses part of the yard as a base for maintenance of way operations on the Northeast Corridor. Two other freight railroads also operate freight trains to and from the yard in the 2020s, including the Providence and Worcester Railroad and Connecticut Southern Railroad. Cedar Hill Yard remains the largest classification yard in Connecticut as of 2022 despite its diminished size. Proposals exist to rebuild portions of the yard, potentially in concert with the construction of the proposed Cross-Harbor Rail Tunnel in New York City or the resumption of car float service across Long Island Sound.

The first instance of Cedar Hill Yard was built in the early 1890s by the New York, New Haven and Hartford Railroad (The New Haven) in and around the Cedar Hill neighborhood of the city of New Haven, on flat lands adjacent to the Quinnipiac River. The yard first opened for service in December 1894, with a capacity of approximately 400 railroad cars. Less than a year later, the new yard caused a dispute between the railroad and its employees. Once Cedar Hill Yard opened, train crews had to stop their trains within the new yard as opposed to the yard in New Haven proper, which reportedly increased their shifts by several hours. Employees demanded extra pay for the longer hours, but the railroad refused, leading several train crews to walk off the job. One railway man was quoted by a local newspaper as saying:

We think that it is no more than fair that extra pay be given us for all work over eight hours for yard men and all over ten hours for through men. Those men who run into New Haven and were ordered to take their trains to Cedar Hill, were done an injustice. It takes at least two hours to sidetrack a train there and get back into the city and I do not blame the men for refusing to do it unless paid for extra time.

Operations at the yard came to a halt on November 21, 1901, when approximately 125 switchmen and brakemen went on strike in solidarity with strikers at Mott Haven. The New Haven's president John M. Hall asserted the strike would quickly end, as the strikers had no specific grievances beyond sympathy for the Mott Haven strikers, who had gone on strike following the abrupt termination of the yard's assistant yard master. The strike came to an end on November 23.

On July 31, 1904, a deadly train collision occurred just outside of Cedar Hill Yard. The New Haven's White Mountain passenger train collided with the rear of a freight train attempting to pull into a siding by the yard, resulting in the death of the White Mountain's engineer, while the train's fireman survived with severe injuries. A coroner found the crew of the freight train criminally responsible for the crash, as they had neglected to send a flagman behind their train to warn the White Mountain, which they knew was due to arrive, that the tracks were not clear. As a result of the crash, operations were changed so that all northbound trains entered the yard at the south end.