A recent oil rush in America is giving local residents some extra bills to add to their bank accounts.

The average income in Mountrail Country, the center of oil production in North Dakota, roughly doubled in five years to $52,027 per person in 2010 because of the recent oil boom hitting the area.

Mountrail County was ranked one of richest U.S. countries, coming in alongside New York City and Marin, Calif., according to Yahoo.

But what caused the recent rise?

In simple terms, there is just so much oil to pass around in North Dakota and so the locals are making some money off of it.

The news site reported that a well drilled under the town of Stanley, N.D., could mean that many residents will receive a small oil royalty check. Others have heard of prosperity the oil boom is bringing North Dakota residents and as a result, Yahoo reported that the population in Stanley has doubled to 3,2000 in the last five years.

Oil royalties refer to funds received based on the amount of oil produced, free of costs except for taxes. It is also defined as the cash value paid to one who has acquired possession of royalty rights, based on gross production from the property.

Some residents in North Dakota do not own mineral rights to the land and so they have not been able to cash out in the recent oil splurge like their neighbors. Land and mineral rights are sometimes sold separately. The owner of the mineral rights receives the royalties.

The oil rush could be creating up to 2,000 millionaires a year in the state, said Bruce Gjovig, founder of the Center of Innovation at the University of North Dakota.

Mountrail is the No. 1 oil producing county in the state, with McKenzie County coming in second. Many residents living in the oil regions receive $50,000 or $60,000 a month in oil royalties, and some more than $100,000.

There is a downside though.

Williston, N.D., Mayor Ward Koeser said the city is dealing with growth problems, spanning from a lack of housing to a need to expand its public works system. Even with that problem, new housing and population studies suggest that Williston will double its population within the next 12 years.

It has not been confirmed, but the reason for the growth might be because people are moving in to the area to try to get in on the oil rush and some checks in their pockets.