US highways 20-29, with branch routes

3-digit "branch" routes are listed under their 2-digit "main" route.  Highways shown in italics have been decommissioned.​

US 20

• US 120
• US 220
• US 320
• US 420

US 21

• US 121 [i] (original)
• US 121 [ii] (future)
• US 221
• US 321
• US 421
• US 521

US 22

• US 122 [i] (original)
• US 122 [ii] (second)
• US 222
• US 322
• US 422 (eastern segment)
• US 422 (western segment)
• US 522

US 23

• US 123 [i] (original)
• US 123 [ii] (current)
• US 223

US 24

• US 124
• US 224

US 25

• US 425 (actually an anomalous number, not a branch of US 25)

US 26

• US 126

US 27

• US 127
• US 227

US 28
US 29

• US 129

Page originally created 1998;
​​last updated Nov. 7, 2016.