Charlyn walks completely around the boundary of a square whose sides are each $5$ km long. From any point on her path she can see exactly $1$ km horizontally in all directions. What is the area of the region consisting of all points Charlyn can see during her walk, expressed in square kilometers and rounded to the nearest whole number?

$\text{(A)}\ 24 \qquad\text{(B)}\ 27\qquad\text{(C)}\ 39\qquad\text{(D)}\ 40 \qquad\text{(E)}\ 42$
1. **Understanding the Problem:**
   Charlyn walks around a square with side length \(5\) km. From any point on her path, she can see exactly \(1\) km horizontally in all directions. We need to find the total area that Charlyn can see during her walk.

2. **Visualizing the Problem:**
   - The square has side length \(5\) km.
   - From any point on the boundary, Charlyn can see \(1\) km in all directions, forming a \(2\) km wide strip around the square.

3. **Calculating the Total Area:**
   - The total area of the square including the \(1\) km visibility strip is a larger square with side length \(5 + 2 \times 1 = 7\) km.
   - The area of this larger square is:
     \[
     7^2 = 49 \text{ km}^2
     \]

4. **Subtracting the Unseen Area:**
   - The central part of the original square (which is not visible from the boundary) has side length \(5 - 2 \times 1 = 3\) km.
   - The area of this central part is:
     \[
     3^2 = 9 \text{ km}^2
     \]

5. **Adjusting for Overlapping Corners:**
   - At each corner of the original square, the visibility regions overlap, forming quarter circles of radius \(1\) km.
   - The area of one quarter circle is:
     \[
     \frac{\pi \times 1^2}{4} = \frac{\pi}{4} \text{ km}^2
     \]
   - There are four corners, so the total area of these quarter circles is:
     \[
     4 \times \frac{\pi}{4} = \pi \text{ km}^2
     \]

6. **Combining the Areas:**
   - The total visible area is the area of the larger square minus the area of the central part plus the area of the overlapping corners:
     \[
     49 - 9 + \pi \approx 49 - 9 + 3.14 = 43.14 \text{ km}^2
     \]

7. **Rounding to the Nearest Whole Number:**
   - The final area, rounded to the nearest whole number, is:
     \[
     \boxed{43}
     \]