By Agence France-Presse
Maria Valles Bonilla waved a small American flag at a ceremony in Washington, her hand on her heart as she pledged allegiance to the United States surrounded by family, including her great-grandchildren.
She was interviewed beforehand by US Citizenship and Immigration Services agents, who determined that she met all the necessary conditions to be naturalized as an American citizen, a spokesman said.
During her interview, Valles Bonilla said her late husband had harbored the dream of becoming American and so she filled out the paperwork and completed the process in his honor.
President Donald Trump has led a virulent campaign targeting illegal immigration, focusing on thousands of migrants making their way on foot toward the United States in the hopes of obtaining asylum.
Many members of the caravan come from El Salvador, fleeing its endemic violence and poverty.