Union members, local councillors, parents and young people marched through the city centre, before listening to speakers including Northampton North MP Sally Keeble.
Doug Nicholls, general secretary of the Community and Youth Workers' Union, which organised the rally, said: "The meeting called for a public inquiry into what the county council has done with the money allocated to youth services."
But on Monday, the council's cabinet was expected to ratify its final budget proposals, including those for youth services.
Youth minister Beverley Hughes wrote to children's services directors last week to warn authorities that the extra 115m represented by the Youth Opportunity Fund and Youth Capital Fund should not be used as a substitute for mainstream services and that core provision should not be cut.
"I don't think (turning youth services into) statutory services is the answer, because we've given local authorities the freedom to make decisions for themselves," she told Young People Now. "We've set national standards for youth services and local authorities will be inspected against those standards. And the education bill will include legislation which will put those standards into place."
- See Leader, p13.