On April 22, 1982 the Imperial Sugar Company dedicated a state historical marker at the Imperial Refinery. (The marker is now stored at the Sugar Land Heritage Foundation.) I found an article in the May 1982 issue of The Imperial Crown covering the dedication ceremony and a summary of the Kempner family's involvement with the company.
Click the image to view the article.
Imperial Refinery State Marker Dedication, March 1982
There are four other state historical markers within Sugar Land's city limits: the Sugar Land Auditorium, Sugar Land (community/town), Main Building on the Texas prison system's Central Unit, and Stafford's Plantation. There is also a Historic Texas Cemetery marker within its precincts: the Imperial Prison Farm Cemetery.