Complex sentence: The cemetery was active from the mid-nineteenth century into the early twentieth century (although some burials took place as late as the 1990s), and as many as 1,000 free and enslaved African Americans are said to be interred here.
Split into simpler sentences: The cemetery was active from the mid-nineteenth century into the early twentieth century (although some burials took place as late as the 1990s). As many as 1,000 free and enslaved African Americans are said to be interred here.