Montgomery County itself does not have laws on knives, but the State of Maryland does that county residents must obey.
To explain, in the United States, we have the type of governmental system such that you start at the top (the US Federal Government) and work your way down to state, then county, then city. When an upper level makes law, all smaller areas under it are subject to that law as well. But when an upper level has no laws on a matter, the next level down may choose to make laws on that matter, or not.
Getting to the heart of the matter, the knife laws of Maryland. The state has two laws that are applicable in the criminal code; Title 4-101 and 4-105.
To sum up in plain English, you many own any knife you wish. There are no laws that control what you may keep in your home. Title 4-105 does make it illegal to SELL switchblades, but the end-result of this law is that you will not find switchblades for sale in Maryland. You may still own them.
The knife carry laws are another matter. Title 4-101 only concerns itself with concealed carry of certain non-gun weapons. Basically, you can carry anything if it's openly carried: switchblades, butterfly knives, bowie knives, daggers, swords, machetes etc. are all technically legal to carry unconcealed and in plain site, so long as they are not used in a threatening manner nor with the intent to harm someone unlawfully.
If you want to carry a knife concealed, there are some guidelines to follow. Title 4-101 specifically declares that "penknives" are not weapons, and thereby are exempt from the law entirely. While the statute does not define "penknife," Maryland's highest court ruled in the 1970s that this word means "any knife with the blade folding into the handle, some very large." This encompasses all common folding knives, assisted opening knives, and butterfly knives. There is no length restriction whatsoever and anyone who tells you different is a liar. So binding was this decision that in 2002, a police officer who ignorantly arrested a man for a concealed folding knife was tried and convicted of False Arrest in federal court, and lost his badge as a result.
It is illegal to carry switchblades and daggers concealed. Regarding single-edged fixed-blade knives, it is actually rather vague. The law does not specifically say it is legal or illegal. Rather, court records show that it is a matter of circumstances under which a person is found having a knife. While a person caught trespassing or breaking into a house with a fixed blade knife may be convicted of carrying a concealed dangerous weapon, a person stopped for a traffic stop is often let go with a verbal warning or the charge dropped before trial. All things to consider.
One laar matter is that in certain counties, it is illegal for a minor (under 18) to be carrying a weapon such as a bowie knife, dagger, sword, etc. between 1 hour after sunset and 1 hour before sunrise. This applies in Anne Arundel County, Baltimore County, Caroline County, Cecil County, Harford County, Kent County, Montgomery County, Prince George's County, St. Mary's County, Talbot County, Washington County, and Worcester County.