In 25 Major League games over parts of three seasons, Williams is a .281 hitter.
Herrera, 25, was signed by the Rockies out of the Dominican Republic in 2010 and had spent his career in that organization. Last season at Triple-A Albuquerque, he batted .278/.351/.394 with three home runs and 27 RBIs.
Mark Sheldon has covered the Reds for MLB.com since 2006, and previously covered the Twins from 2001-05. Follow him on Twitter @m_sheldon and Facebook and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.