| Alexander MacWilliam Sr. | |
| Birth Date: | 25 May 1891[1] |
| Birth Place: | Edinburgh, Scotland[2] |
| Death Date: | August 13, 1966[3] |
| Death Place: | Indian River County, Florida |
| Restingplace: | Crestlawn Cemetery, Vero Beach, Florida |
| Residence: | Vero Beach, Florida |
| Office1: | Mayor of Vero Beach, Florida |
| Order1: | 4th, 7th and 9th |
| Term Start1: | December 15, 1927 |
| Term End1: | December 10, 1935 |
| Predecessor1: | Bayard Redstone |
| Successor1: | Anthony W. Young |
| Term Start2: | December 13, 1939 |
| Term End2: | December 11, 1947 |
| Predecessor2: | Wiley F. Cox |
| Successor2: | Merrill P. Barber |
| Term Start3: | December 14, 1949 |
| Term End3: | October 16, 1951 |
| Predecessor3: | Merrill P. Barber |
| Successor3: | Louis G. Burger |
| Office4: | Member of the Florida House of Representatives from Indian River County |
| Term Start4: | 1933 |
| Term End4: | 1935 |
| Predecessor4: | Charles A. Mitchell |
| Successor4: | Eli C. Walker |
| Term Start5: | 1945 |
| Term End5: | 1953 |
| Predecessor5: | J. Hubert Graves |
| Successor5: | Sherman N. Smith Jr. |
| Party: | Democratic |
| Occupation: | landscape architect[4] |
| Spouse: | Delia Jeanette Flaherty MacWilliam (m. April 26, 1920)[5] |
| Children: | Alexander, Peter, Robert, Edgar, William, Helen, Joan, Barbara |
| Battles: | World War I |
| Branch: | United States Army |
| Unit: | 313th Machine Gun Battalion |
| Awards: | Purple Heart Distinguished Service Cross |
Alexander Duncan "Mac" MacWilliam Sr. (May 25, 1891 – August 13, 1966) was the mayor of Vero Beach, Florida from 1927 to 1935, from 1939 to 1947, and from 1949 to 1951, he also served in the Florida House of Representatives from Indian River County in the 1933, 1945, 1947, 1949 and 1951 sessions.
MacWilliam was born in Edinburgh, Scotland, and immigrated with his family to Cleveland, Ohio, when he was 18.[2]
During World War I, serving with the 313th Machine Gun Battalion, 80th Division[6] at the Battle of Meuse-Argonne, MacWilliam was shot in both legs while rescuing a trapped and wounded soldier.[2] He was also the victim of a mustard gas attack, and suffered continuing health problems because of it.[4] His doctor mentioned to him that he was investing in land in Florida, and MacWilliam decided to join him.[4] In 1919, he moved from Ohio to Vero Beach, and he went on to supervise the construction of the golf course at Riomar.[4] He met Jeanette Flaherty at the golf course, and married her in 1920.[4]
In 1927, he was elected mayor. He supported the proposal to split off Indian River County from St. Lucie County.[4] MacWilliam established the Indian River Mosquito Control Board, and introduced height restrictions on buildings.[4]