With a polygon on a map within the US, get estimated population of area

I need to be able to create a polygon on a map and get estimate population for the selected area. Essentially, I would need something similar to [login to view URL] Ideally, the estimation tool should return fairly reliable results similar to what can be found on here [login to view URL] When you go to the website, use the polygon tool then click on the polygon then click the population icon to get an estimate population count. Take a look at the screenshots for visuals.