This is far and away the question I get asked most. Somebody buys a cart, gets it home, and then wonders whether they can drive it down to the mailbox without getting a ticket. The honest answer is that it depends on where you live, and the rules are not the same in Kalispell as they are in Whitefish or out in the county.
The short version
A standard golf cart is not built for public streets in Montana. In state law a golf cart is a vehicle designed for use on a golf course with an average speed of less than 15 mph, and out of the box it cannot be titled, registered or plated. That does not mean you can never drive it off your property, but it does mean the permission has to come from somewhere specific.
Where the permission comes from
There are two answers that matter for a standard cart.
Local ordinance. This is the important one, and it has a statute behind it. Montana Code Annotated 61-8-391 gives counties, cities and towns the authority to pass ordinances permitting golf carts on their streets. Montana does not allow it statewide, your town has to have opted in.
Where a community has opted in, you generally need a valid driver's license and a one time registration decal, which at the time of writing is $25. Standard golf carts are otherwise exempt from titling, registration and mandatory liability insurance.
That same statute also sets out equipment a cart has to carry when it is driven on a street under one of these ordinances: headlamps, a taillamp, a reflector, stop lamps, a horn, and a mirror that gives the driver a view of the road behind. Plenty of carts leave the factory without some of that. Fitting lights, blinkers and mirrors is ordinary work and I do it all the time.
These ordinances are town by town and they change. Call your city clerk and ask directly, because secondhand information about this is usually wrong.
Private property. On your own land, do what you like. This is where most carts in the Flathead live and it is why most people never need to worry about any of the above.
What I would actually tell a neighbor
If you want to drive around your property and down a quiet private road, you are fine and you always were. If you want to drive into town, find out first whether your town has actually opted in, and get the cart properly equipped before you go, because a half sorted cart with a light bar zip tied to the roof is the one that gets pulled over.
And check with your own town. I can tell you what the general rules are but I cannot tell you what your city council decided last spring.
One more thing worth saying plainly: I am a mechanic, not a lawyer, and this is a summary rather than legal advice. The Montana MVD at mvdmt.gov is the authority on titling and registration, and your city clerk is the authority on whether your town allows carts on its streets.
Questions about your specific cart? Call me at 406.270.9346.