Old Harford Road, one of the oldest continuously used rights-of-way in central Maryland, United States, is a southwest–northeast thoroughfare in northeast Baltimore City and eastern Baltimore County.

Present-day Old Harford Road begins in the 6000 block of Harford Road in the Hamilton section of Baltimore City and continues nearly 5+1⁄2 miles northeast through the Parkville and Carney areas of Baltimore County to near the Big Gunpowder Falls north of Cub Hill. Old Harford Road serves as an alternate route to both Harford Road (Maryland Route 147) and Perring Parkway (Maryland Route 41), and carries between 10,000 and 16,500 vehicles per day. Old Harford Road, like Harford County, was named for Henry Harford (1758–1834), the son of Frederick Calvert, 6th Lord Baltimore, and the last Proprietary of Maryland prior to the American Revolutionary War.

Old Harford Road follows a curving path along relatively high land bordering streams that feed the upper Chesapeake Bay, including Chinquapin Run. This suggests its likely origin as an Indian trail that subsequently was adopted by settlers to convey farm products from northeastern Baltimore County, Harford County, and southern Pennsylvania to the port of Baltimore in the late 18th century.

The name "Old Harford Road" appears on area maps dating to at least 1850 (see, for example, map display in the Meeting Room of the Baltimore County Public Library in Towson, Maryland). In particular, the 1850 J. C. Sidney map indicates that today's Satyr Hill Road, Cromwell Bridge Road north of Satyr Hill, and Glen Arm Roads collectively were known as Old Harford Road. Four sections of the Sidney map, annotated to highlight the location of today's Old Harford Road with respect to area roads of today—and to the Old Harford Road of 1850—are provided below. Nineteenth century deeds to two notable properties in the area, obtained by the late Baltimore County historian John W. McGrain, substantiate Sidney's depiction of Old Harford Road. The "Shanklin House" (or "Forest Hall"), once located at present-day 8906 Satyr Hill Road, and "Serendipity", on present-day Glen Arm Road, north of Glen View, are both listed as being located on "The Old Harford Road". The Shanklin House once served as a tavern, and its 1845 deed notes that the property was located on "the well-traveled main road". Old Harford Road also appears on Robert Taylor's 1857 map of Baltimore County (not shown here). The map depicts "Carroll's Factory", a woolen mill later converted to a flour mill, where the road crossed the south bank of Gunpowder Falls. Some of the structures of this property remain extant as a private residence along Cub Hill Road, just east of today's Cromwell Bridge Road (originally, Old Harford Road).

The Old in Old Harford Road most likely dates to the period shortly after the completion of the Harford Turnpike by private road-building interests in 1816. Harford Turnpike, now known as Harford Road (Maryland Route 147), was constructed as a more direct route between present-day Mt. Vista Road and what became the Hamilton section of Baltimore (i.e., to today's intersection of Harford and Old Harford Roads). Further evidence that today's Cromwell Bridge and Glen Arm Roads comprise part of the original Old Harford Road is provided by the 1829 edition of the Laws of the Maryland General Assembly; Chapter 224 describes the construction of a county roadway (likely today's Cub Hill Road) that was to extend from "... the Old Harford Road near Cromwell's Bridge (Gunpowder Falls) to the Harford Turnpike". A complicating bit of information regarding the use of the moniker "Old", however, is provided by a genealogical reference to a tavern that was said to have been located on Old Harford Road "near the Long Green Valley" around 1776. Why the prefix "Old" would have been used at that early date is uncertain. If the reference is accurate, it could reflect that a displacement of the original Harford Road right-of-way already had been made prior to the construction of the Harford Turnpike in 1816.

While the name "Old Harford" may be traced with certainty to only the first third of the nineteenth century, the right-of-way itself is older. For example, the 1794 map of Maryland by Dennis Griffith (shown below) depicts a thoroughfare extending northeast from the central part of Baltimore City into Harford County, Maryland. This road is distinct from nearby roads that evolved into parts of today's Belair Road (U.S. Route 1), Philadelphia Road (Maryland Route 7), and York Road (Maryland Route 45). The shape and orientation of the unnamed right-of-way bears close resemblance to that of today's Old Harford Road. Anthony Finley's 1824 map of Maryland, schematically depicts a route of travel extending north-northeast from Baltimore City to the Coopstown area of western Harford County (near today's Jarrettsville). Subsequent editions of his map and others (e.g., see those by Thomas Cowperthwait (1865) and Thomas Letts (1883) also shown below) extend the route northeastward to the Susquehanna River at McCall's Ferry in York County, Pennsylvania --- and even beyond the Susquehanna into adjacent Lancaster County. These routes likely incorporated parts of today's Long Green Pike and Pleasantville Road in Baltimore and Harford Counties.

Through the first half of the twentieth century, various published maps—including state-issued topographic maps (see example below)—indicate that the portion of today's Cub Hill Road between Old Harford Road and Cromwell Bridge Road / Glen Arm Road was known as "Old Harford Road." This observation, in conjunction with the more widely-known fact that all or parts of today's Satyr Hill, Cromwell Bridge, and Glen Arm Roads were once labeled "Old Harford," suggests that Old Harford Road is an example of a "braided" thoroughfare. "Braided" roads were those whose names were conferred informally (i.e., by local usage) to separate but roughly parallel roadway segments that temporarily diverged but subsequently rejoined. Together, the briefly-separate rights-of-way constituted a single main path of travel. In the case of Old Harford Road, it appears that parts of today's Satyr Hill, Cromwell Bridge, and Cub Hill Roads --- along with that part of Old Harford Road between Satyr Hill and Cub Hill - together once constituted a braided right-of way. With the official naming of rural thoroughfares by municipal governments following the advent of motor vehicles in the early 1900s, unique names typically were conferred to "braided" roadway segments to minimize traveler confusion.

Available records suggest that, like similar roads in the region, Old Harford Road likely remained gravel-covered as late as World War I. Some sections, however, may have been macadamized by that time. Asphalt pavement was most likely introduced in the Hamilton and Parkville sections beginning in the 1920s. The "Second Report on the Highways of Maryland," included as part of Volume 4 of the 1902 Report of the Maryland State Geological Survey notes that the Ninth District of Baltimore County spent $1124 to "top-dress" part of Old Harford Road with gravel stone in 1901. Comparable or greater amounts were also spent the same year on Hillen Road, Arlington Avenue, Hamilton Avenue, and Roland Avenue. By 1927, aerial views of eastern Baltimore County (see below) suggest that all parts of today's Old Harford Road had been paved.