In 1855 Washington King became the seventeenth mayor of St. Louis.
Since 1835 most Mayors had devoted much time to bringing railroads to St. Louis. Mayor King continued these activities. In his message to the Council he recommended additional aid to the Ohio and Mississippi Railway to help unite the City with the East. In 1855 Mayor King and former Mayors Kennett and Wimer were on board a 14 car train that brought the Midwest its first major rail disaster. The Pacific Railroad was completed from St. Louis to Jefferson City and on November first, a large group of civic leaders started the seven hour trip to the State Capitol. It was a stormy day, and near Herman, the Gasconade River bridge gave way with many cars crashing into the flooding river. Thirty-one passengers died, and Mayor King and previous Mayor Wimer were injured.
The City's population doubled from 77,860 in 1850 to 160,773 in 1860. This increase was partly due to the annexation of 1856. In that year the City took in surrounding territory of 9 and one-half square miles. Since 1841 the City had occupied 14 square miles. The western limit was extended from Eighteenth Street to Grand Avenue. The outlying towns of Bremen and the Second Municipality of St. Louis were taken in. The Missouri Legislator had passed a Law in 1855 providing for this extension. Thus municipal services had to be extended to a new area about twice the size. State Law made the effective date of the annexation March 31, 1856. The Mayor urged more street paving. The Waterworks was expanded with the completion of a second reservoir at Twentieth and Benton Streets. Mr. King recommended that the Mayor's term should extend through a period of from three to five years.