Sections — The 640-Acre Building Block

In the Public Land Survey System, the section is the fundamental unit of land division. Each section is nominally 1 mile square and contains 640 acres. Every township in the PLSS grid contains 36 sections, arranged in a specific numbered pattern that has remained unchanged since the early surveys of the 1780s.

If you read a legal land description like Sec 12, T4N R5E, you are looking at a section reference — one specific 640-acre square within a township. Understanding how sections are numbered, how they fit within the township grid, and where the system deviates from the ideal is essential for anyone working with PLSS land descriptions.

36 Sections per Township

A standard township is 6 miles on each side — a 36-square-mile area. This area is divided into a grid of 6 rows and 6 columns, producing 36 sections. Each section is 1 mile on each side (5,280 feet) and contains 640 acres.

The 640-acre section can be further subdivided into quarter sections of 160 acres, quarter-quarter sections of 40 acres, and even smaller aliquot parts. But the section is the level at which the original government survey was conducted — section corners and quarter-section corners were the monuments set in the field by survey crews.

The Serpentine Numbering Pattern

Sections are not numbered in a simple left-to-right, top-to-bottom pattern. Instead, they follow a serpentine (back-and-forth) sequence that starts in the northeast corner of the township and snakes back and forth to end in the southeast corner.

Here is the standard section numbering layout:

┌──────┬──────┬──────┬──────┬──────┬──────┐
│      │      │      │      │      │      │
│   6  │   5  │   4  │   3  │   2  │   1  │
│      │      │      │      │      │      │
├──────┼──────┼──────┼──────┼──────┼──────┤
│      │      │      │      │      │      │
│   7  │   8  │   9  │  10  │  11  │  12  │
│      │      │      │      │      │      │
├──────┼──────┼──────┼──────┼──────┼──────┤
│      │      │      │      │      │      │
│  18  │  17  │  16  │  15  │  14  │  13  │
│      │      │      │      │      │      │
├──────┼──────┼──────┼──────┼──────┼──────┤
│      │      │      │      │      │      │
│  19  │  20  │  21  │  22  │  23  │  24  │
│      │      │      │      │      │      │
├──────┼──────┼──────┼──────┼──────┼──────┤
│      │      │      │      │      │      │
│  30  │  29  │  28  │  27  │  26  │  25  │
│      │      │      │      │      │      │
├──────┼──────┼──────┼──────┼──────┼──────┤
│      │      │      │      │      │      │
│  31  │  32  │  33  │  34  │  35  │  36  │
│      │      │      │      │      │      │
└──────┴──────┴──────┴──────┴──────┴──────┘

Follow the numbers to see the serpentine path:

1. Row 1 (top): Sections 1-6, numbered right to left (east to west), starting at the northeast corner
2. Row 2: Sections 7-12, numbered left to right (west to east)
3. Row 3: Sections 13-18, numbered right to left again
4. Row 4: Sections 19-24, numbered left to right
5. Row 5: Sections 25-30, numbered right to left
6. Row 6 (bottom): Sections 31-36, numbered left to right, ending at the southeast corner

This pattern means that Section 1 is always in the northeast corner and Section 36 is always in the southeast corner. Section 6 is in the northwest corner and Section 31 is in the southwest corner.

Why Serpentine?

The serpentine pattern reflects how surveys were actually conducted in the field. Survey crews would work across a row, then reverse direction for the next row, minimizing backtracking. The numbering follows the path the surveyors walked.

How Sections Are Referenced

A section is identified by its number within a specific township. The complete reference includes the township and range:

In many western states, section numbers appear on county road maps, topographic maps, and even road signs. If you drive through rural Oklahoma, Kansas, or Colorado, you will often see section markers along county roads.

Format Variations

Different documents and industries use slightly different formats for section references:

• Standard: Sec 12 or Section 12
• Abbreviated: S12 or §12
• Oil and gas: Often placed first in compact notation: 12-4N-5E (Section 12, Township 4 North, Range 5 East)
• BLM: Section 012 (zero-padded in databases)
• Deed language: "Section Twelve (12)" — written out with the number in parentheses

Regardless of format, the section number always refers to the same physical location within its township.

School Sections: 16 and 36

When Congress designed the PLSS, it reserved specific sections in every township for the support of public education. Section 16 was designated as the "school section" — land that was set aside to fund local schools, either through direct use or through the revenue from its sale or lease.

As new states were admitted to the Union, Congress expanded this grant. States admitted after 1848 typically received both Section 16 and Section 36 as school lands. Some later-admitted states (Arizona, New Mexico, Utah) received four sections per township: Sections 2, 16, 32, and 36.

This history has practical consequences today. In many western states, Sections 16 and 36 are still managed by state land trusts and generate revenue for education through grazing leases, mineral rights, and land sales. If you encounter a Section 16 or 36 in a title search, it may have a different ownership history than surrounding sections.

Fractional Sections

Not every section contains exactly 640 acres. Several factors can create fractional sections — sections that are larger or smaller than the standard:

Convergence of Meridians

Because lines of longitude converge toward the poles, townships become slightly narrower as you move north. The PLSS compensates for this with standard parallels (correction lines), but the convergence still affects the westernmost and northernmost sections in a township. By convention, the shortage or excess in acreage is absorbed by sections along the north and west edges of the township — specifically Sections 1-6 (the top row) and Sections 6, 7, 18, 19, 30, and 31 (the west column).

Section 6, in the northwest corner, bears the greatest adjustment because it sits at the intersection of both the north and west correction edges.

Natural Boundaries

When a river, lake, state boundary, or reservation border crosses a township, it creates fractional sections along the boundary. These fractional sections are often designated with "lot" numbers rather than standard quarter-section descriptions. A title document might reference "Lot 3 of Section 4" rather than a standard aliquot part.

Survey Errors

Early surveys were conducted with chain and compass under difficult field conditions. Measurement errors were common, and once a survey was accepted and land was sold based on it, the original survey controlled — even if later measurements showed the section was not exactly 640 acres. As a legal principle, the monuments set by the original surveyor define the section boundaries, regardless of the actual acreage.

Sections on the Ground

Original survey crews marked section corners and quarter-section corners with physical monuments — wooden posts, stone mounds, bearing trees (trees scored with markings indicating the direction and distance to the nearest corner), or later, iron pipes and brass caps.

Many of these original monuments have been found, preserved, and referenced by modern surveyors. In agricultural areas, section corners often coincide with road intersections — rural roads in PLSS states frequently follow section lines, creating the mile-grid road pattern visible from the air across much of the Midwest and Great Plains.

The Bureau of Land Management (BLM) maintains records of the original survey plats and field notes through the General Land Office (GLO) records collection. These historical documents show the original section corners, the terrain the surveyors encountered, and any notes about the land's character.

Sections in Practice

Understanding section numbering matters for practical, everyday tasks:

• Drilling permits reference sections: a permit for Sec 22-9N-15W tells you exactly where the well is located
• Crop insurance reports use section references to identify damaged fields
• Timber sales describe harvest areas by section and quarter section
• Title searches trace ownership from the original government patent through subsequent deeds, all described by section
• Emergency services in rural areas often use section references to locate incidents when there are no street addresses

Knowing that Section 1 is in the northeast corner and Section 36 is in the southeast — and being able to visualize the serpentine pattern in between — lets you quickly orient yourself on any township plat map.

From Section to Parcel

A 640-acre section is a large area — a full square mile. Most land transactions deal with smaller parcels. The next level of subdivision divides each section into quarter sections of 160 acres, and those quarters can be further divided into 40-acre quarter-quarter sections.

Understanding how these subdivisions work — and how to read the notation that describes them — is covered in Quarter Sections and Aliquot Parts.

For the big picture of how sections fit into the overall PLSS hierarchy, see How the Public Land Survey System Works.

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