Moody's Investors Service downgraded Westchester County, N.Y. to Aa1 from Aaa on Nov. 20, affecting $1 billion in debt.
In addition Moody's downgraded the county's lease revenue bond rating to Aa2 from Aa1, affecting $99 million.
Moody's has a stable outlook on the ratings.
The downgrade of the GO rating was connected to the county's narrowed financial position in recent years, said Moody's analyst Robert Weber and senior analyst Christopher Coviello.
The county has narrowing reserves and a trend of structurally imbalanced operations, they said. It is also exposed to economically volatile sales tax revenues.
On the other hand, it has a large and diverse tax base. It also has a strong socio-economic profile.
The lease revenue bond rating is based on the lease's satisfactory legal provisions and essentiality of the financed projects.
Fitch Ratings and Standard & Poor's rate the county's GO debt AAA.