From how far away is a Wi-Fi connection accessible?

It all depends on how you set it up. Most home based systems will reach a house or two down the block, but what is between you and the source can really affect that. A signal will travel a lot farther through open air than if it has to get past metal pipes. So it is really hard to give a difinitive answer. There are some special antennas you can buy (and some you can make) that will extend the range, but the most important factor is what lies BETWEEN you and the signal. That is what will limit the range the most. At my home, I can get a weak signal from a house a block away. It isn't very reliable or fast at such a low strength though. If you think of 40 feet as a reliable limit you will be fine. That doesn't mean it can't go farther... just that you can't count on it being reliable, it may work fine... or not