The tower that you see today northwest of downtown Des Moines off Keo Way on 9th Street isn't the original channel 8 tower. That tower was at 9th & Pleasant, where the headquarters of the Principal Financial Group are today. I don't know when the Principal complex was built. The construction of that complex forced KCCI to relocate its studios. The actual transmitting site for channel 8 moved to Alleman decades ago. KCCI (it may have still been KRNT then) was the last of the four legacy TV stations (the others: WOI, KDIN, WHO) to move to Alleman. The story I've heard is that KRNT was originally going to join the other three stations of the time at the first Alleman tower. But the stations drew straws for tower position and KRNT got the lowest position. Instead, they decided to build their own tower nearby. The tower you see in Des Moines proper today is mostly to support an STL. KFMG-LP is on that tower as well.
Assuming that the KDPS-FM tower is going away soon (I'll be in Des Moines in early October so I can see for myself at that time), the KCCI tower may be the last one standing in that part of the city.