The trails in Cedar Falls are very safe, they go all around town - including Hartman Nature Reserve and George Wyth State Park which is connected to Waterloo as well. These are part of the Cedar Valley Lakes Trail System, link here:
http://www.inhf.org/iowatrails/cedar...akes-intro.htm
There are 2 major rail trails in the area, including the Waverly Rail Trail from Denver to Waverly, as well as the Cedar Valley Nature Trail from Evansdale (Waterloo) to Hiawatha (Cedar Rapids)
They are beautiful in autumn and when the weather is nice the trails do get pretty busy - make sure when you come up on someone to pass them you say "on your left!"

Many people use them for cross-country skiing during the winter season as well.
If the previous posted link doesn't provide the information you are seeking, here is another one to click!
Cedar Valley Lakes Trail Network