It is a pretty much accepted fact by the scientific community. The incidence of colon cancer and small bowel cancer is higher in our group than in the population not suffering from crohn/UC. There is a lot of factors that come in line though, certain countries found that there was no worse incidence while other had like, north america and UK says its more frequent while other european studies has shown that the risk was the same. We can therefore suppose there are lifestyle, food and such that comes in list not only CD. There are more risks of developing colon cancer when its colonic involvement of the disease, patients with small bowel CD have increased risks of small bowel cancer too.
If my memory is good I believe there is a fivefold overall relative risk, but then again, the lenght of the disease is implied, the severity of the inflammation comes in line, the maintenance treatment too, so there is a lot to consider. I don't know if it may reassure you but there is up to a 25fold increase risk of lung cancer in smokers, use of sun tanbeds doubles the risk of skin cancers. I mean, yes, the rates are more important, but it is less frequent than other cancers related to bad habits.
It's also important to remember that we get screened way more often than the average Joe and hence, as for any other cancers' type, early diagnosis give great advantage to the patient. Also, it's not because the risk is increased that we all end up suffering from cancer.