This problem primarily requires understanding the formula for the angle between two vectors and the definition of vector projection. By using the formula for the angle between two vectors, we find the cosine of the angle $\theta$ between $\overrightarrow{a}$ and $\overrightarrow{b}$. Applying the definition of vector projection, we calculate the projection of $\overrightarrow{a}$ onto $\overrightarrow{b}$ as $|\overrightarrow{a}|\cos{\theta} = 5\times \frac{2}{\sqrt{5}} = 2\sqrt{5}$.

Step 1: Calculate the dot product of $\overrightarrow{a}$ and $\overrightarrow{b}$.
$\overrightarrow{a} \cdot \overrightarrow{b} = (-3)(-2) + (4)(1) = 10$.

Step 2: Determine the magnitudes of $\overrightarrow{a}$ and $\overrightarrow{b}$.
$|\overrightarrow{a}| = \sqrt{(-3)^2 + (4)^2} = \sqrt{25} = 5$,
$|\overrightarrow{b}| = \sqrt{(-2)^2 + (1)^2} = \sqrt{5}$.

Step 3: Calculate the cosine of the angle $\theta$ between $\overrightarrow{a}$ and $\overrightarrow{b}$.
$\cos{\theta} = \frac{\overrightarrow{a} \cdot \overrightarrow{b}}{|\overrightarrow{a}| |\overrightarrow{b}|} = \frac{10}{5\sqrt{5}} = \frac{2}{\sqrt{5}}$.

Step 4: Calculate the projection of $\overrightarrow{a}$ onto $\overrightarrow{b}$.
$\boxed{\text{Projection of } \overrightarrow{a} \text{ onto } \overrightarrow{b} = |\overrightarrow{a}|\cos{\theta} = 5 \times \frac{2}{\sqrt{5}} = 2\sqrt{5}}$.