The first section of MD 23 to be paved was the part of the Old York Turnpike from MD 138 to MD 439, which was improved as a 12-foot-wide (3.7 m) macadam state-aid road by 1910.
 The portion of MD 23 from Hickory to Jarrettsville was designated one of the original state roads by the Maryland State Roads Commission in 1909.
 The state road was constructed with a 14-foot-wide (4.3 m) macadam surface from Hickory to Grafton Shop Road in 1910, from Morse Road to Jarrettsville in 1914, and between Grafton Shop Road and Morse Road in 1915.
 Another section of 12-foot-wide (3.7 m) macadam road was constructed under state aid from south of Norrisville to the Pennsylvania state line by 1915.
 The highway from Jarrettsville to MD 138 was under construction as a concrete road by 1919 and completed in 1921.
 The final portion of MD 23, also paved in concrete, was completed from MD 439 to south of Norrisville in 1923.
 MD 23 was one of the original state-numbered highways designated by the roads commission in 1927.
 The state highway was widened to a width of 20 feet (6.1 m) from Hickory to Jarrettsville by 1930.

Jarrettsville Road was replaced by East–West Highway, which was under construction by 1961 and completed in 1963.
 The MD 23 designation was moved to the new highway and Jarrettsville Road was immediately transferred to county maintenance.
 At its eastern end, East–West Highway was constructed to tie into the Bel Air Bypass that was completed in 1965 and was proposed to continue to east of Hickory.
 Close to its eastern end, MD 23 curved south to an intersection with Granary Road.
 MD 23 turned east onto Granary Road for its eastern terminus at US 1 (now US 1 Business).
 East–West Highway continued south as MD 23A; at Bynum Road, MD 23A became a one-lane ramp that joined the Bel Air Bypass.
 In 2000, the Hickory Bypass was completed; US 1 was moved to the new bypass and US 1 Business was extended along US 1's old route through Hickory.
 As part of the same project, MD 23 was extended east to a new terminus at the Hickory Bypass.
 East–West Highway's curve to the south was replaced with a perpendicular intersection with MD 23A, which was renamed Water Tower Way, extended north to new MD 23, and gained a ramp from northbound US 1 at its southern end.
 The portion of Granary Road that formed MD 23's terminus was designated MD 23B.  Both MD 23A and MD 23B were transferred to Harford County maintenance in 2002.
 MD 23's roundabout at Commerce Road in Forest Hill was constructed in 2008.
The first section of MD 23 to be paved was the part of the Old York Turnpike from MD 138 to MD 439, which was improved as a 12-foot-wide (3.7 m) macadam state-aid road by 1910.  The portion of MD 23 from Hickory to Jarrettsville was designated one of the original state roads by the Maryland State Roads Commission in 1909.  The state road was constructed with a 14-foot-wide (4.3 m) macadam surface from Hickory to Grafton Shop Road in 1910, from Morse Road to Jarrettsville in 1914, and between Grafton Shop Road and Morse Road in 1915.  Another section of 12-foot-wide (3.7 m) macadam road was constructed under state aid from south of Norrisville to the Pennsylvania state line by 1915.  The highway from Jarrettsville to MD 138 was under construction as a concrete road by 1919 and completed in 1921.  The final portion of MD 23, also paved in concrete, was completed from MD 439 to south of Norrisville in 1923.  MD 23 was one of the original state-numbered highways designated by the roads commission in 1927.  The state highway was widened to a width of 20 feet (6.1 m) from Hickory to Jarrettsville by 1930.
Jarrettsville Road was replaced by East–West Highway, which was under construction by 1961 and completed in 1963.  The MD 23 designation was moved to the new highway and Jarrettsville Road was immediately transferred to county maintenance.  At its eastern end, East–West Highway was constructed to tie into the Bel Air Bypass that was completed in 1965 and was proposed to continue to east of Hickory.  Close to its eastern end, MD 23 curved south to an intersection with Granary Road.  MD 23 turned east onto Granary Road for its eastern terminus at US 1 (now US 1 Business).  East–West Highway continued south as MD 23A; at Bynum Road, MD 23A became a one-lane ramp that joined the Bel Air Bypass.  In 2000, the Hickory Bypass was completed; US 1 was moved to the new bypass and US 1 Business was extended along US 1's old route through Hickory.  As part of the same project, MD 23 was extended east to a new terminus at the Hickory Bypass.  East–West Highway's curve to the south was replaced with a perpendicular intersection with MD 23A, which was renamed Water Tower Way, extended north to new MD 23, and gained a ramp from northbound US 1 at its southern end.  The portion of Granary Road that formed MD 23's terminus was designated MD 23B.  Both MD 23A and MD 23B were transferred to Harford County maintenance in 2002.  MD 23's roundabout at Commerce Road in Forest Hill was constructed in 2008.
Maryland Route 23