There will actually be two main shut off valves at the typical suburban residence. One valve will be at the city water meter (usually located in a buried box near the street). This city valve is usually under a locked lid, but with commonly available tools it can be accessed and shut off in the event of an emergency.
This will shut off the water to the entire property - including any yard sprinkler system and fire suppression system. Although, some larger properties have a separate meter for the irrigation system.
By plumbing code, a main shut off valve is also required near where the main water supply comes into the house. This is the valve designed for the homeowner to use and have easy access to. By shutting off this valve, just the house water system will be turned off - not the separate irrigation system or conventional fire suppression system.
Most commonly in our area, this valve is located in the front flower bed where the water supply pipe (which is buried in the yard) goes underneath the slab foundation to the first “manifold”. Or, in newer homes, the main shut off valve may be located behind a wall panel in the garage or in a utility room.
In areas with higher pressure, a special valve called PRV (Pressure Reducing Valve) is installed next to the main shut off valve.
Know where this valve is, make sure it is in good working condition, and have all occupants of the home practice shutting off the water in the event of a plumbing emergency to prevent damage to the home. This valve will either be a lever-handle ball valve or a round-handle gate valve (more on these later).