Through his marriage he became a brother-in-law to Andries de Graeff and Lambert Reynst, burgomasters of Amsterdam and also to Gerard Bicker (I) van Swieten.
In 1664, Cornelis Geelvinck bought the fiefdoms of Castricum and Croonenburg for 33,000 and 25,000 guilder respectively, which brought him earnings and the right to make appointments.
In August 1666 the Amsterdam government sent him as "vigilant gentleman" to Den Helder, where an English raid was feared.
In November 1672 the States of Holland ordered him to carry away the hay and peat from Uithoorn and the surrounding towns, so that they would not fall into the hands of the French army that had occupied Utrecht.
In 1684 Geelvinck had to receive stadholder William III of Orange in the townhall, but the prince refused to stop his horse and passed the town hall at a gallop.