WASHINGTON — Montgomery County, Maryland, gets to keep its membership in the best credit club, maintaining AAA bond ratings for 2018 from all three Wall Street bond rating agencies.

Fitch, Moody’s and Standard & Poor’s all affirmed the AAA rating for the county, and all keep their outlook for Montgomery County as “stable.”

“The county’s tax base will experience additional growth because of economic expansion and diversification. Going forward we will continue to monitor the county’s ability to maintain financial flexibility and reserve levels that are compliant with its 10 percent fund balance target,” Moody’s wrote in reaffirming its Montgomery County rating.

The higher a county’s bond rating, the lower the interest rate the county will pay on its obligations.

Surrounding counties — including Arlington, Fairfax, Loudoun, Prince William in Virginia and Prince George’s in Maryland — all have the highest AAA ratings from the credit rating agencies.

In July of this year, the District itself made Wall Street history when Moody’s Investors Service assigned its top AAA credit rating to the D.C.’s outstanding general obligation bonds.

It is the first time in history the District has had a AAA rating.

Standard & Poor’s and Fitch bond rating services also upgraded the District’s general obligation bond rating from AA to AA+, the second-highest ratings issued by the two agencies.

Two decades ago, D.C. bonds were rated “junk.”