In 1864 James S. Thomas became the twenty-third Mayor of St. Louis.
James S. Thomas was elected Mayor as a Republican, in April of 1864, to fill the unexpired term of Mayor Chauncey I. Filley. He continued as Mayor until 1869, the second longest period of service of a St. Louis Mayor to that time.
The City was growing rapidly. Its population increased from 160,773 in 1860 to 310,864 in 1870. Mayor Thomas advocated City purchase of the Gas Works but was unable to bring this about. Thomas did see his program for the improvement of public health enacted. Further development of the Sewer System included provision for the Mill Creek, Rocky Branch and Arsenal Street sewers. He took the leadership in establishing a new Waterworks System. In 1867 construction of a well designed plant was started at Bissell's Point. This plant consisted of a low service station to pump the water from the river to four sediment basins and a high service station to pump the clear water to Compton Hill reservoir at Grand and Lafayette Avenues. The East Grand Water Tower was a part of the whole project. This Tower was completed in 1870.
Cholera had broken out again in 1866. The Mayor appointed sanitary committees in each ward. The mortality rate decreased shortly. In March of 1869 the State Legislature authorized the Mayor to appoint a new Board of Health. This new board organized and started it's work on March 16, 1869.
The present house numbering system was approved by Mayor Thomas on December 18, 1865. North and south streets were numbered from Market Street. East and west streets were numbered from the wharf. Each block west, north or south represented one hundred numbers, as distinguished from the old system where numbers had been assigned without regard to blocks.