Pujols, 27, is a native of the Dominican Republic but has resided in the U.S. since he was 16. He attended high school and junior college in the Kansas City area before being drafted by the Cardinals. He currently makes his home outside of St. Louis.
He was confirmed as a citizen on Wednesday in a small public ceremony in downtown St. Louis. According to an Associated Press report, the ceremony was attended by about "two dozen" friends and family members.
It's been a busy and momentous several months for Pujols. The Cardinals won the World Series in October, and shortly afterward he received his first Rawlings Gold Glove Award. In January he traveled to the Dominican on a humanitarian mission to help provide medical care and education for impoverished children in his home country.
Shortly after being sworn in, Pujols headed south to Florida for Spring Training. Always an early arriver, he will begin working out more than a week before the required reporting date for position players.
Matthew Leach is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.