Arkansas Highway 166 is a designation for two state highways in Randolph County, Arkansas. The southern segment of 7.97 miles (12.8 km) runs from Old Davidsonville State Park

Old Davidsonville State Park

Old Davidsonville State Park preserves the site of the frontier town of Davidsonville. The town was founded in 1815 and rapidly became the most important town in northeast Arkansas Territory, but was abandoned by the 1830s...

 to Pocahontas

Pocahontas, Arkansas

Pocahontas is a city in Randolph County, Arkansas, United States, along the Black River. According to 2006 Census Bureau estimates, its population of the city is 6,765. The city is the county seat of Randolph County....

. A northern segment of 14.57 miles (23.4 km) runs north from US 62

U.S. Route 62 in Arkansas

U.S. Route 62 is a U.S. highway running from El Paso, Texas northeast to Niagara Falls, New York. In the U.S. state of Arkansas, the route runs 329.9 miles from the Oklahoma border near Summers east to the Missouri border in St. Francis, serving the northern portion of the state...

/US 67

U.S. Route 67 in Arkansas

U.S. Route 67 in Arkansas runs from Texarkana to the Missouri state line in Northeastern Arkansas.-Route description:U.S. Route 67 runs parallel to Interstate 30 from Texarkana to Benton, where it then runs concurrent with I-30 to North Little Rock. It then runs east, concurrent with I-40, for...

 to the Missouri

Missouri

Missouri is a US state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. With a 2010 population of 5,988,927, Missouri is the 18th most populous state in the nation and the fifth most populous in the Midwest. It...

 state line.

Old Davidsonville State Park to Pocahontas

AR 166 begins at Old Davidsonville State Park

Old Davidsonville State Park

Old Davidsonville State Park preserves the site of the frontier town of Davidsonville. The town was founded in 1815 and rapidly became the most important town in northeast Arkansas Territory, but was abandoned by the 1830s...

 in southwest Randolph County. The route runs north to meet US Route 62

U.S. Route 62 in Arkansas

U.S. Route 62 is a U.S. highway running from El Paso, Texas northeast to Niagara Falls, New York. In the U.S. state of Arkansas, the route runs 329.9 miles from the Oklahoma border near Summers east to the Missouri border in St. Francis, serving the northern portion of the state...

 in south Pocahontas

Pocahontas, Arkansas

Pocahontas is a city in Randolph County, Arkansas, United States, along the Black River. According to 2006 Census Bureau estimates, its population of the city is 6,765. The city is the county seat of Randolph County....

. The route is entirely two-lane, undivided.

Pocahontas to Missouri

AR 166 begins at US 62/US 67

U.S. Route 67 in Arkansas

U.S. Route 67 in Arkansas runs from Texarkana to the Missouri state line in Northeastern Arkansas.-Route description:U.S. Route 67 runs parallel to Interstate 30 from Texarkana to Benton, where it then runs concurrent with I-30 to North Little Rock. It then runs east, concurrent with I-40, for...

 in east Pocahontas. The route runs north to meet AR 115

Arkansas Highway 115

Arkansas Highway 115 is a state highway of that runs in Sharp, Lawrence, and Randolph Counties.-Route description:AR 115 begins at US 167/AR 58 in Cave City running with AR 58 north. The route continues northeast to meet AR 117 in Smithville. AR 115 arrows north to Imboden where it meets US 62/US...

 at Stokes and AR 328

Arkansas Highway 328

Arkansas Highway 328 is a state highway of that runs in Randolph and Clay Counties.-Route description:AR 328 begins at AR 251 between Ingram and Attica. It runs northeast to meet AR 115/AR 166 in Maynard. The route exits Maynard heading due east before angling south to Reyno. AR 328 meets and...

 in Maynard

Maynard, Arkansas

Maynard is a town in Randolph County, Arkansas, United States. The population was 426 at the 2010 census.Settled in the late 19th century, Maynard is home to the Maynard Pioneer Museum and Park. Behind the Maynard Community Center is a unique jail. Built in 1936, its door is made of wagon wheel...

. AR 166 then trails north through Supply and Minorea to the Missouri

Missouri

Missouri is a US state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. With a 2010 population of 5,988,927, Missouri is the 18th most populous state in the nation and the fifth most populous in the Midwest. It...

 state line, where it terminates at Missouri supplemental routes A/Y

Missouri Supplemental Route

A supplemental route is a state secondary road in the U.S. state of Missouri, designated with letters. Supplemental routes were various roads within the state which the Missouri Department of Transportation was given in 1952 to maintain in addition to the regular routes...

.

Major intersections

Mile markers reset at concurrencies.
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| align=center colspan=4 | AR 166 begins at US 62/US 67
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| align=center colspan=4 | concurrency north, 4.9 miles (7.9 km)
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