How Many State Borders Exist in the United States?

The question "How many state borders?" has no single answer—it depends entirely on what you count as a border.

Counting Methodologies

1. Unique State Pairs Sharing a Border: 109

Each unordered pair of states that touch counts once. (e.g., NY-PA = 1 border).
Calculation: Sum of each state's neighbors ÷ 2.
Range: 1 (HI, ME) to 8 (TN, MO). Total unique adjacencies = 109.

2. Border Segments (County-Level): ~1,500+

Each county-to-county boundary along a state line = 1 segment. Used for GIS, redistricting, jurisdictional administration.

3. Linear Miles/Kilometers

• Total interstate boundary length: ~43,000 miles (69,000 km)
• Longest: TX-NM (~1,241 mi), MT-WY (~1,100 mi)
• Shortest: DC-MD (~10 mi), RI-CT (~45 mi land)

4. The "59" Figure Explained

The source's "59 state borders including DC" likely counts:
• 50 states × 1 "border" each = 50 (nonsensical)
• OR: Number of states with international borders (18) + states with coastline (23) + DC = 42 (still not 59)
• OR: Number of state boundary lines on a simplified map (projection-dependent)

Most plausible: A misinterpretation or specific dataset artifact. 109 unique state-pair borders is the standard topological answer.

Special Cases

• Four Corners: One point (AZ/CO/NM/UT) — 4 states, 6 pairwise borders converge.
• Water Borders: Lake Erie, Lake Michigan, Long Island Sound, Potomac, Mississippi — complex adjudication.
• Maritime Boundaries: Extend 3-12 nm offshore (Submerged Lands Act).

For precision: specify what you're counting. For trivia: 109 state-pair borders.