Chickens are not currently permitted in Rockville. I believe the environment committee tried change that a year ago January but nothing happened from what I tell. If enough got behind a push to allow hens we should at least be able to the city adopt the county regs.
I think that within Rockville city limits, it may be illegal. Outside of the city limits, it is a different story.
I would urge you to sign up for the Montgomery County Backyard Chickens group. They have an email list which has some good info about the subject.
While the county did not make keeping chickens explicitly legal, they did leave the law as currently written.
The important part of the ordinance is the section which reads, "Any accessory building or structure used for the housing, shelter, or sale of animals or fowl other than a household pet must be a minimum of 25' from a lot line and a minimum of 100' from a dwelling on another lot.
Italics added, but the point is that pets have always been exempt, but the county has for years decided to ignore this and tell everyone that it is simply illegal. Go figure.
Getting mine this spring, as pets, which is what they are to our family, so no deceit. I also registered with the state agriculture department, which on the registration form lists "hobby/pet" as a reason for keeping chickens, so that is the box I checked.