Mailout/Mailback The vast majority of households (about 90% of the population) will receive a census form in the mail via the US Postal Service. This partnership with the USPS has continued since 1970, when the first mailout/mailback US Census was conducted. We ask that you fill it out and mail it back by April 1.
Update/Leave In areas of the country (about 9% of the population) where mail is not delivered to residences uniformly, census staff will visited each housing unit, update our list of addresses, and leave a census form package in a plastic bag at the entrance door of the unit. This is the technique will we use in the Gulf Coast areas that were heavily affected by hurricane damage and are in the middle of their recovery.
Update/Enumerate Just like in remote Alaska, there are parts of the US (about 1% of the population) that both don’t uniformly receive mail at their residence and are far from any town. Some of these have demonstrated very low return rates of questionnaires in the past. In these areas, we will visit each housing unit and take a face-to-face interview with those in the household.
Large Military Installations At big military installations (e.g., Fort Bragg, NC) field work is coordinated with a military representative, and the Census staff is escorted to each housing unit to deliver the questionnaires. The military representative ensures that all questionnaires are returned.
This map is from Dr. Groves' blog, showing where the different methods are being employed. If you can't read the legend, here it is:
Purple = Mailout/mailback; Tan = Update/Leave; Green = Update/Enumerate; (Dark Green = Remove Area Update & Update/Enumerate)