The Maine DOT classifies "state highways" as those "which primarily serve arterial or through traffic". They are maintained by MDOT except for those in urban areas, which are maintained by the municipality involved. Not all designated state highways carry route numbers, and not all numbered highways are designated state highways. Below is a list of all unnumbered designated state highways in rural and suburban areas (sorted by county), as well as those in urban areas which are at least 2 miles in length. Some supplemental designated highways (for instance, exit ramps) are not included. The internal "inventory route" number (if applicable) and length is listed in brackets.

A second class, "state aid" highways, also exists in which (outside urban areas) MDOT maintains roads in the summer and the municipality does in the winter. There are hundreds (if not thousands) of designated unnumbered state aid roads, and no attempt will be made to document them on this site.

Androscoggin County

• Court St., Auburn. Portion between Minot Ave. and Union St. (1.86 mi)
• Turner St., Auburn. (2.57 mi)
• Mount Auburn Ave./Veterans Memorial Bridge/Russell St., Auburn to Lewiston. (3.08 mi)

Aroostook County

• Robinson Rd./Old Houlton Rd., Blaine to Bridgewater. (IR 2577, 3.94 mi)
• Bog Rd., Caribou to Limestone. (IR 5000 and 894, 6.40 mi)
• West Gate Rd., Caribou. (IR 534, 2.76 mi)
• Boundary Rd., Hamlin. Connects US 1A with border. (IR 718, 0.91 mi)
• Cote Rd., Limestone. (parts of IR 5000 and 439, 3.28 mi)
• Long Rd., Limestone. (IR 548, 1.36 mi)
• Ward Rd., Limestone. (part of IR 457, 2.55 mi)
• Bridge Ave., Madawaska. Connects US 1 with border. (IR 2603, 0.27 mi)
• Castle Hill Rd., Mapleton to Washburn. (IR 471, 3.76 mi)
• Hughes Rd., Mapleton. (part of IR 475, 3.50 mi)
• High Meadow Rd., Perham. Portion between Route 228 and Tangle Ridge Rd. (part of IR 872, 2.20 mi)
• Tangle Ridge Rd./Erickson Rd./Margison Rd., Perham to Woodland. (IR 513, 12.07 mi)
• Carson Rd., Perham to Woodland. (IR 3003, 6.17 mi)
• Oakfield-Smyrna Rd., Smyrna to Oakfield. Portion between US 2 and I-95. (part of IR 1407, 1.47 mi)
• Bridge St., Van Buren. Connects US 1 with border. (IR 2248, 0.28 mi)

Cumberland County

• Bucknam Rd., Falmouth. (0.56 mi)
• Riverside St., Portland. (1.82 mi)
• Warren Ave., Portland to Westbrook. (2.84 mi)
• Haigis Pkwy., Scarborough. Connects Maine Turnpike exit 42 and US 1. (1.44 mi)
• Broadway, South Portland. Portion between Maine Turnpike Approach and Route 77 at Casco Bay Bridge. (3.82 mi)
• Maine Mall Rd., South Portland. (1.85 mi)
• Maine Turnpike Approach, South Portland. Freeway connection between Maine Turnpike exit 45 and US 1. Listed as Route 703 in some documents. (1.89 mi)
• Scarborough Connector, South Portland to Scarborough. Freeway connection between I-295 exit 2 and US 1. (2.10 mi)
• Spring St./Cummings Rd., Westbrook to Scarborough. (3.60 mi)

Franklin County

• none

Hancock County

• none

Kennebec County

• Father Curran Bridge/Water St., Augusta. (0.46 mi)

Knox County

• none

Lincoln County

• Village St., Jefferson. (IR 582, 0.65 mi)
• Main St., Waldoboro. (IR 536, 1.75 mi)
• Old Route 1, Waldoboro. (IR 1312, 3.11 mi)
• Depot St., Waldoboro. Portion between Main St. and US 1. (IR 555, 0.52 mi)

Oxford County

• Railroad St., Rumford to Mexico. (0.28 mi)
• Androscoggin River Bridge, Mexico to Peru. (part of IR 416, 0.41 mi)
• Main St., Norway. Portion between Routes 117 and 26. (IR 1622, 0.30 mi)

Penobscot County

• Broadway, Bangor. Portion between US 2 and I-95. Formerly part of Route 15. (1.28 mi)
• Griffin Rd., Bangor. Portion between Routes 222 and 15. (1.66 mi)
• Hogan Rd., Bangor. Portion between US 2 and I-95. (1.37 mi)
• Main St., Brewer. Portion between I-395 and Route 9. Formerly part of Route 15. (0.74 mi)
• Parkway South, Brewer. Portion between I-395 and US 1A. (0.56 mi)
• Penobscot Valley Parkway, Chester. Connects I-95 exit 227 with Route 116 and US 2. (IR 1887, 2.54 mi)
• Kelly Rd., Orono. Portion between I-95 and US 2. (0.71 mi)
• Stillwater Ave., Orono to Old Town. Portion between I-95 and US 2A. (0.72 mi)

Piscataquis County

• Hudson Ave./Pleasant Ave., Guilford to Sangerville. (part of IR 356, 1.43 mi)

Sagadahoc County

• State Rd., West Bath to Bath. (IR 1062, 2.37 mi)
• New Meadows Rd., West Bath. Portion between US 1 and State Rd. (part of IR 536, 0.68 mi)

Somerset County

• Somerset Ave., Pittsfield. (part of IR 466, 1.03 mi)

Waldo County

• Main St., Belfast. (0.76 mi)
• High St., Belfast. (2.08 mi)
• Sears Island Rd., Searsport (2.25 mi)

Washington County

• North St., Calais. Connects US 1 with Milltown border crossing. (IR 1483, 0.22 mi)
• Future border crossing connector, Calais. (IR 928, 0.58 mi)
• Milford Rd., Indian Twp. to Grand Lake Stream. (IR 822, 10.44 mi)
• Beals Island Bridge, Jonesport to Beals. (IR 1131, 0.52 mi)
• Port Rd., Machiasport. (IR 321, 5.90 mi)

York County

• Biddeford Spur, Biddeford. Connects Route 111 at Maine Turnpike exit 32 to US 1. (0.85 mi)
• Province Lake Rd., Parsonsfield. Part of New Hampshire Route 153. (IR 1353, 2.00 mi)
• Old Alfred Rd., Waterboro. (part of IR 451, 1.97 mi)
• I-95 Connector, York. Connects Maine Turnpike exit 7 to US 1. (IR 1423, 0.52 mi)

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