It depends, if you have received a tetanus shot in the last ten years, the answer is no. If however, it has been longer than ten years, or you can't remember when you received the shot, then yes you need one.
Clostridium tetani is an organism that is ubiquitous. It is a gram positive spore forming bacillus and a normal inhabitant of many surroundings. If someone sustains an injury in which the skin is broken, they are susceptible to contracting this organism and should receive the tetanus shot.
Left untreated you may develop paralysis of the masseter muscles, sardonic smile, and "lockjaw". Symptoms may include difficulty swallowing, profuse sweating, and hypotension.
Tetanus is an infectious disease caused by bacteria that live in the soil. Clostridium tetani can live for many years in the soil as spores. When a person gets a wound, the spores infect the wound. The spores activate and develop into gram positive bacteria which release toxins that attack the muscles. Tetanus causes uncontrollable muscle spasms, lock jaw, and can even affect the muscles that are used for breathing.
Types of injuries that are tetanus prone are puncture wounds, frostbite, surgery, abscesses, childbirth, and IV drug users.
The tetanus vaccine is commonly given during infancy. It is important to get a tetanus booster every ten years.
Tetanus is a disease that is most often associated with rust (like rusty nails) - but actually it is caused by bacteria - Clostridium tetani. It is just that the bacteria causing tetanus is most often found growing outdoors - and rust on a nail would provide a prime living surface for this bacteria.
If you cut your foot deeply on something metalic or dirty and you haven't had a tetanus shot within the last 10 years (or you cannot remember your last shot) you will probably receive one to be safe.
The shot itself is harmless - however the disease is nasty. It has been called "lock jaw" because it basically causes muscles to go into a constant state of contraction, which I imagine would be very painful.
If you have not received a tetanus shot within the last five years, and the object you cut your foot with was metal and rusty, or the cut is dirty I would suggest contacting your physician. Getting a tetnus shot will keep you from contracting this disease. Whenever you have a dirty cut, animal bite, or puncture wound, check to see when you last had a booster shot.
It depends what you cut your foot with....if it was metal that cut your foot, you would need to check and see when you had your last tetanus shot, if it should fall outside of the acceptable range, then you would need to get one. If you cut your foot with something else, no.