International Roissy-Charles de Gaulle airport is only at 25 km of Senlis. The connection for Senlis is possible by the bus Picardie-Roissy.
A taxi from CDG airport to Senlis will cost around €40.
Train / Bus
There's no train station in Senlis, the nearest train stations are Chantilly or Creil, then you will need to take a bus to Senlis.
The nearest TGV station is Roissy - Charles de Gaulle airport.
The motorway A1 runs between Paris and Brussels, exit 8: Senlis.