That was always the nice thing about the old 7490 decade counter (old in that it was within the first offerings Signetics had for their 7400-series TTL). The 7490 (and all its offspring and several similar counters) consisted of a divide-by-5 and a divide-by-2 counter. If you ran the output of the 2 into the 5, you had standard BCD output but a non-square decade output. Or you could run the output of the 5 into the 2 and get the same decade result with a 50% duty cycle at the sacrifice of not being able to use the ABCD outputs to drive a display decoder because things would be all scrambled up.
If you want a decade divider AND a square output (adding a binary divider to the output of a decade divider will give you a very inconvenient divide-by-20 and you'd have to remember to convert your counter display), consider modifying a decade or 4-bit binary counter to do a divide-by-five and then add a binary counter to the end. Two or three chips (depending up the chip type) for the output you might desire, although there's no need to preserve a square input for a frequency counter.
Remember that if you use a prescaler like that, you destroy your counter's resolution by a factor of 10. With a 1-second gate time, you'd normally read the frequency to the nearest Hertz. With a prescaler added and using the same gate time, you'll be reading the frequency to the nearest 10 Hertz.
If your use for this circuit is as a prescaler to extend the upper frequency of a counter, don't forget that the chips you use for this "front end" need to have a frequency capability that is 10 times that of the counter's capability for maximum range or your prescaler will limit your top end.
Dean