| State Highway 121 | ||||
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| Route information | ||||
| Maintained by TxDOT | ||||
| Length: | 85.563 mi (137.700 km) | |||
| Existed: | by 1939 – present | |||
| Major junctions | ||||
| Southwest end: |
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| Northeast end: |
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| Highway system | ||||
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Business State Highway 121-D |
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| Location: | Randolph |
| Length: | 1.734 mi (2.791 km) |
| Existed: | 1990–present |
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Business State Highway 121-H |
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| Location: | Dallas and Denton counties |
| Length: | 8.486 mi (13.657 km) |
| Existed: | 1999–present |
I-820 from Richland Hills to North Richland Hills
I-635 in Grapevine![]()
I-35E / US 77 in Lewisville
Dallas North Tollway in Plano
US 75 from McKinney to Melissa
US 69 in Trenton