The U.S. Census Bureau reports that data are not available to release a list of most common surnames as of the last census, but the chart below shows the change from 1990 to 2000.
In 2000, the U.S. Hispanic population was 34 million, or about 12% percent of the total, according to figures from the Pew Hispanic Center; so, considering the increase for 2011 "“ too nearly 52 million, or a jump to 17%, you can imagine a few more Hispanic surnames, or at least a greater frequency, among the most common last names in America nowadays.
In 2000, the number of individuals whose last name was Smith was 2,376,206; those whose last name was Garcia numbered 858,289 - the eighth-most prevalent surname - followed closely by Rodriguez at 804,240.
Surnames make a difference, in politics and beyond. Here's an earlier Next America story about the possibility of bias in the voting booth.
Meantime, our sister publication, Quartz, offers an explanation from a man formerly named Crouch who has assumed the maiden name of his fiancé's maternal grandmother.