Relay was the first stop on the Baltimore & Ohio Railroad west of its terminus in Baltimore, Maryland. When the railroad was first created in 1830 the cars were pulled by horses, and they would stop at Relay to change teams for the next segment to Endicot Mills. The railroad would eventually extend West to Harpers Ferry in 1836 and to the Ohio River at Wheeling in 1852. This provided a fast and reliable route between the Ohio River Valley and the Chesapeake Bay area.

In 1833 a branch began building South to Washington D.C., splitting off fromt thee main line at Relay. It was completed in 1835, and was the only railroad to Washington until after the Civil War. The junction of these two vitally important rail lines made Relay a major strategic location in the Civil War.

Relay House was built in 1830 by the Baltimore & Ohio Railroad at Relay. The three story building combined a station, hotel, restaurant and tavern. Passengers who were transferring between the branches would often stay the night before transferring to their connecting train. Since dining cars had not yet been developed, trains would stop so that passengers could disembark and have a meal and a drink before resuming their trip.

Relay House during the Civil War

In the early days of the war pro-Confederate mobs in Baltimore attacked Federal troops moving through the city to protect Washington. Federal forces abandoned the city, cutting Washington off from the North. Union General Benjamin Butler brought troops in by landing at Annapolis and taking the Baltimore & Ohio north along the Washington Branch. Thirty carloads of men from the Eighth New York State Militia and Sixth Massachusetts Infantry Regiment reached Relay on May 5 and occupied the junction and its surrounding area.On May 13 Union troops used Relay as the jump off point for the occupation of Baltimore.

A permanent camp of over 2,000 men with artillery and fortification and was established around Relay and would remain until the end of the war. Trains would be searched at Relay House for Confederate contraband such as buttons, ammunition and pistols. Despite a number of scares, no Confederate invasion or raid ever captured Relay House.

Relay House still exists today but it is not the original, having been rebuilt after a fire. Due to the fire and modifications over the the years it has greatly changed its appearance from the original.