The BBC's West Africa correspondent, John James, says Liberians regard the US as an old friend.
Everything in Liberia, which was founded by free slaves from America more than 150 years ago, draws its inspiration from the US "motherland" - including the flag, the government and local architecture, he says.
But Liberian infrastructure remains in a desperate state, with electricity and water being rare commodities.
Cheque book out?
"It is impressive the way that Liberia has decreased its debt, which was run up of course during years of conflict, and has had a high rate of GDP growth over the last years," Mrs Clinton said during a press conference with Mrs Johnson-Sirleaf.
"And the government is inclusive especially for women which I take great pleasure in noting," she added.
Our correspondent says that if Liberians will be disappointed if they imagine Mrs Clinton has come with an open cheque book.
Mrs Clinton has repeatedly called on the countries she has visited on this tour to end corruption and encourage Africans to seize the opportunities available.
She was expected to deliver the same message to the Liberian parliament.
At her previous stop in Nigeria, she urged officials to embrace broad political reform and ease tensions that have led to sectarian violence and disrupted energy production in the Niger Delta.
The secretary of state is due to leave Liberia late on Thursday for Cape Verde, from where she will fly home to Washington on Friday.
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