More like until the 1930s. The last time a black majority district sent a Republican to Congress was in 1932. In 1934, the voters replaced him with a black Democrat and no Republican has been elected to Congress since in a black majority district. FDR converted most blacks to the Democratic Party very early in his administration.
Florida should elect her as governor!
You’re half right. By the mid 1930s, most Northern Blacks had become majority Democrat (although there was still a substantial enough presence of Black Republicanism, about 1/4th in some areas, that lasted for 3 more decades). This was not, however, true of Southern Blacks. That did not occur until the 1960s. Because most Southern Blacks were barred from voting until that latter point (since the late 1890s), there were virtually zero Black officeholders above town level, except in rare cases where some managed to make it to town or city councils. In my hometown of Nashville, one of the few pre-CRA officeholders of the 1960s on the City Council was Z. Alexander Looby, and Looby was a Republican (although because of the changing climate, he did endorse LBJ in ‘64). The radicalization of the mid to late ‘60s pushed both regions, with some occasional exceptions, into the 90% camp for the Dems.