To complement to ohwilleke answer:
The original SPLC report for the data in ohwilleke's answer is available online and lists its methodology as well as all monuments and streets/schools that were considered.
Their graphic shows the same tendency of monuments being built in a time of racial struggles:
The Washington Post notes that many of these monuments where not politically neutral monuments at the time they were created; instead, the neo-confederate and white supremacist group United Daughters of the Confederacy pushed for them:
The group responsible for the majority of these memorials was the United Daughters of the Confederacy (UDC), among the most influential white women’s organizations in the South in the late 1800s and early 1900s.
The Washington Post also puts this in a historical context:
The 1890s, when the UDC was founded and monument building began in earnest, was a decade of virulent racism across the South. Not content to disenfranchise black men, Southern whites went on a lynching spree. [...]
Amid that brutality, the pace of Confederate monument construction quickened. The UDC and other like-minded heritage organizations were intent on honoring the Confederate generation and establishing a revisionist history of what they called the War Between the States. According to this Lost Cause mythology, the South went to war to defend states’ rights, slavery was essentially a benevolent institution that imparted Christianity to African “savages,”[...]. The Daughters regarded the Ku Klux Klan [...] as a heroic organization, necessary to return order to the South. Order, of course, meant the use of violence to subdue newly freed blacks.
During the era of Jim Crow, Confederate monuments could be placed most anywhere. Some were in cemeteries or parks, but far more were erected on the grounds of local and state courthouses. These monuments, then, not only represented reverence for soldiers who fought in a war to defend slavery, they also made a very pointed statement about the rule of white supremacy: All who enter the courthouse are subject to the laws of white men.
The Business Insider interviewed various historians who agree that the statues were an attempt at historical revisionism:
Soon enough, however, "... public monuments became a central means of rewriting history from the Confederate perspective [...]
Whittenburg said the monuments tend to come from attempts by the political and business elite to "re-enforce or reinvigorate their claim to authority."