The equation of the given parabola is:
\[
y^2 = x.
\]
This is a standard parabola of the form \( y^2 = 4ax \), where the vertex is at the origin \( (0, 0) \) and the focus is at \( (a, 0) \).
Step 1: Comparing the equation \( y^2 = x \) with \( y^2 = 4ax \), we find that \( 4a = 1 \), so:
\[
a = \frac{1}{4}.
\]
Step 2: The length of the latus rectum of a parabola is given by the formula \( 4a \). Therefore, the length of the latus rectum is:
\[
4a = 4 \times \frac{1}{4} = 1.
\]
Thus, the length of the latus rectum is 1.
Therefore, the correct answer is option (D).