smc

With about $230$ million people and under $4$ million square miles, there are about $60$ people per square mile. Since a square mile is about $(5000\text{ft}{)}^2=25$ million square feet, that gives approximately $\frac{25}{60}$ of a million square feet per person. $\frac{25}{60}$ is approximately half, so the answer is approximately half a million, which is $\boxed{500,000}$.